[Installer] Upgrade the installer from WiX3 to WiX5 (#40877)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request
Background: The current PowerToys installer is built using Wix3, which
has now been deprecated. To improve security, service quality, and
community support, we’re upgrading the installer to Wix5.

Implementation:
Created Wix5-based projects(PowerToysSetupVext and
PowerToysSetupCustomActionsVNext) within the installer while retaining
the existing Wix3 project. Both versions are built to generate separate
installation packages. The Wix3-related code will be removed after
successful release testing confirms no issues.

Special case:
Wix5 has removed the property for 'ShowFilesInUse'. Now, whenever a file
is in use during installation, a FilesInUse pop-upwill automatically
appear asking for the next step. To ensure this doesn't interfere with
scenarios that require silent installation (e.g. Winget method), we’ve
handled it using the bafunction approach.



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## PR Checklist

- [ ] Closes: #xxx
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

---------

Co-authored-by: Jerry Xu <n.xu@outlook.com>
Co-authored-by: Kai Tao <69313318+vanzue@users.noreply.github.com>
Co-authored-by: leileizhang <leilzh@microsoft.com>
Co-authored-by: Kai Tao (from Dev Box) <kaitao@microsoft.com>
Co-authored-by: vanzue <vanzue@outlook.com>

tools/build/build-installer.ps1

@@ -7,7 +7,7 @@ This script automates the end-to-end build and packaging process for PowerToys,
 - Restoring and building all necessary solutions (CmdPal, BugReportTool, etc.)
 - Cleaning up old output
 - Signing generated .msix packages
-- Building the WiX-based MSI and bootstrapper installers
+- Building the WiX v5 (VNext) MSI and bootstrapper installers
 
 It is designed to work in local development.
 The cert used to sign the packages is generated by 
@@ -21,9 +21,12 @@ Specifies the build configuration (e.g., 'Debug', 'Release'). Default is 'Releas
 .PARAMETER PerUser
 Specifies whether to build a per-user installer (true) or machine-wide installer (false). Default is true (per-user).
 
+.PARAMETER InstallerSuffix
+Specifies the suffix for the installer naming (e.g., 'wix5', 'vnext'). Default is 'wix5'.
+
 .EXAMPLE
 .\build-installer.ps1
-Runs the installer build pipeline for ARM64 Release (default).
+Runs the installer build pipeline for x64 Release with default suffix (wix5).
 
 .EXAMPLE
 .\build-installer.ps1 -Platform x64 -Configuration Release
@@ -33,12 +36,16 @@ Runs the pipeline for x64 Release.
 .\build-installer.ps1 -Platform x64 -Configuration Release -PerUser false
 Runs the pipeline for x64 Release with machine-wide installer.
 
+.EXAMPLE
+.\build-installer.ps1 -Platform x64 -Configuration Release -InstallerSuffix vnext
+Runs the pipeline for x64 Release with 'vnext' suffix.
+
 .NOTES
 - Make sure to run this script from a Developer PowerShell (e.g., VS2022 Developer PowerShell).
 - Generated MSIX files will be signed using cert-sign-package.ps1.
 - This script will clean previous outputs under the build directories and installer directory (except *.exe files).
 - First time run need admin permission to trust the certificate.
-- The built installer will be placed under: installer/PowerToysSetup/[Platform]/[Configuration]/User[Machine]Setup 
+- The built installer will be placed under: installer/PowerToysSetupVNext/[Platform]/[Configuration]/User[Machine]Setup 
   relative to the solution root directory.
 - To run the full installation in other machines, call "./cert-management.ps1" to export the cert used to sign the packages.
   And trust the cert in the target machine.
@@ -47,7 +54,8 @@ Runs the pipeline for x64 Release with machine-wide installer.
 param (
     [string]$Platform = 'x64',
     [string]$Configuration = 'Release',
-    [string]$PerUser = 'true'
+    [string]$PerUser = 'true',
+    [string]$InstallerSuffix = 'wix5'
 )
 
 # Find the PowerToys repository root automatically
@@ -114,8 +122,7 @@ function RestoreThenBuild {
     RunMSBuild $Solution '/m'
 }
 
-Write-Host ("Make sure wix is installed and available")
-& (Join-Path $PSScriptRoot "ensure-wix.ps1")
+# WiX v5 projects use WixToolset.Sdk via NuGet/MSBuild; a separate WiX 3 installation is not required here.
 
 Write-Host ("[PIPELINE] Start | Platform={0} Configuration={1} PerUser={2}" -f $Platform, $Configuration, $PerUser)
 Write-Host ''
@@ -154,8 +161,8 @@ try {
 
 RunMSBuild 'installer\PowerToysSetup.sln' '/t:restore /p:RestorePackagesConfig=true'
 
-RunMSBuild 'installer\PowerToysSetup.sln' "/m /t:PowerToysInstaller /p:PerUser=$PerUser"
+RunMSBuild 'installer\PowerToysSetup.sln' "/m /t:PowerToysInstallerVNext /p:PerUser=$PerUser /p:InstallerSuffix=$InstallerSuffix"
 
-RunMSBuild 'installer\PowerToysSetup.sln' "/m /t:PowerToysBootstrapper /p:PerUser=$PerUser"
+RunMSBuild 'installer\PowerToysSetup.sln' "/m /t:PowerToysBootstrapperVNext /p:PerUser=$PerUser /p:InstallerSuffix=$InstallerSuffix"
 
 Write-Host '[PIPELINE] Completed'