[PreviewPane] Fix form positioning issues (#34035)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request

This PR aims to fix some positioning issues of the form used as preview
handler.
It fixes the following issues:
1. The floating window, detached from Explorer that sometimes appears:
#33491 #27475 #24985
2. The **CoreWebView2 members cannot be accessed after the WebView2
control is disposed** crash: #27276
3. `PowerToys.*.PreviewHandler.exe` process leak

### Repro steps for issue 1
- Navigate through files in a folder invoking their preview handler
- Minimize/Restore Explorer quickly (spam WIN+D usually works)
- 2 weird issues happen:
  - Some `PowerToys.*.PreviewHandler.exe` processes are leaked
- Some `PowerToys.*.PreviewHandler.exe` are started with a `NULL` `HWND`

![Screenshot 2024-07-27
**200207](https://github.com/user-attachments/assets/5cb6c857-ad93-422a-8c5b-47bd1c492dce)

This happens because
[IPreviewHandler::DoPreview](https://learn.microsoft.com/windows/win32/api/shobjidl_core/nf-shobjidl_core-ipreviewhandler-dopreview)
is called multiple times and sometimes before calling
[IPreviewHandler::SetWindow](https://learn.microsoft.com/windows/win32/api/shobjidl_core/nf-shobjidl_core-ipreviewhandler-setwindow).

When the managed previewer try to set the parent of the form to the
`NULL` `HWND`, the desktop window is used instead, resulting in the
floating preview window being displayed.
Reference:
https://learn.microsoft.com/windows/win32/api/winuser/nf-winuser-setparent#parameters


5d77874382/src/modules/previewpane/common/controls/FormHandlerControl.cs (L136)

### Repro steps for issue 2
- Preview a file
- Restart `explorer.exe` process
- Make sure `PowerToys.*.PreviewHandler.exe` is leaked and still running
- Preview the same file again
- Preview is displayed (another process is launched)
- Minimize Explorer

What happens here is that the form of the old process have an invalid
`HWND` as parent but receive the `SetRect` for some reason.

<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist

- [x] **Closes:** #33491 #27475 #24985 #27276
- [ ] **Communication:** I've discussed this with core contributors
already. If 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

<!-- Provide a more detailed description of the PR, other things fixed
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

- Don't start preview pane process when `HWND` is `NULL`
- Terminate the preview pane process when setting parent fails
- Prevent leaking processes closing them when a new preview is requested
- Fixed an issue where PDF and SVG previews weren't updated after
restoring Explorer
- Added some error handling in the `UpdateWindowBounds` method of the
managed preview
- Terminate the preview pane when the `SetRect` event is received but
the parent `HWND` has become invalid

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

- Manually tested all preview panes also using multiple Explorer windows
- Validated that when Explorer is minimized/restored the preview is
updated
- Tested the preview pane resize
- Validated that no window, no taskbar icon and no errors appear on both
repro steps

src/modules/previewpane/GcodePreviewHandler/Program.cs

@@ -36,15 +36,24 @@ namespace Microsoft.PowerToys.PreviewHandler.Gcode
                     Rectangle s = new Rectangle(left, top, right - left, bottom - top);
 
                     _previewHandlerControl = new GcodePreviewHandlerControl();
-                    _previewHandlerControl.SetWindow(hwnd, s);
+
+                    if (!_previewHandlerControl.SetWindow(hwnd, s))
+                    {
+                        return;
+                    }
+
                     _previewHandlerControl.DoPreview(filePath);
 
                     NativeEventWaiter.WaitForEventLoop(
                         Constants.GcodePreviewResizeEvent(),
                         () =>
                         {
-                            Rectangle s = default(Rectangle);
-                            _previewHandlerControl.SetRect(s);
+                            Rectangle s = default;
+                            if (!_previewHandlerControl.SetRect(s))
+                            {
+                                // When the parent HWND became invalid, the application won't respond to Application.Exit().
+                                Environment.Exit(0);
+                            }
                         },
                         Dispatcher.CurrentDispatcher,
                         _tokenSource.Token);