Dock: dock visual nits and bits (#45873)

## Summary of the Pull Request

- Improves vertical (left/right) dock layout:
  - Dock items are not clipped;
  - Items with label(s) are stretched to full width;
  - Items without label(s) are centered.
- Top button is in the absolute corner to make clicking to it easier.
- Dock items now have a min width and height 32px.
- Removes a duplicate "No background" label in the expander body on the
Dock settings page.

## Pictures? Pictures!
Vertical layout:
<img width="175" height="1439" alt="image"
src="https://github.com/user-attachments/assets/4f11d9e9-405f-4d9a-8dee-4c8912b88c7c"
/>

Horizontal layout:
<img width="5119" height="49" alt="image"
src="https://github.com/user-attachments/assets/8420ef26-575e-4427-8db8-f9793e3b3572"
/>



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## PR Checklist

- [ ] Closes: #xxx
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **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

<!-- 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

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

src/modules/cmdpal/Microsoft.CmdPal.UI/Controls/ScrollContainer.xaml

@@ -141,10 +141,10 @@
             Grid.Column="1">
             <ScrollViewer
                 x:Name="scroller"
-                HorizontalScrollBarVisibility="Hidden"
+                HorizontalScrollBarVisibility="Disabled"
                 HorizontalScrollMode="Enabled"
                 SizeChanged="Scroller_SizeChanged"
-                VerticalScrollBarVisibility="Hidden"
+                VerticalScrollBarVisibility="Disabled"
                 VerticalScrollMode="Disabled"
                 ViewChanging="Scroller_ViewChanging">
                 <Grid x:Name="ContentGrid">
@@ -188,9 +188,9 @@
             <VisualStateGroup x:Name="OrientationStates">
                 <VisualState x:Name="HorizontalState">
                     <VisualState.Setters>
-                        <Setter Target="scroller.HorizontalScrollBarVisibility" Value="Hidden" />
+                        <Setter Target="scroller.HorizontalScrollBarVisibility" Value="Disabled" />
                         <Setter Target="scroller.HorizontalScrollMode" Value="Enabled" />
-                        <Setter Target="scroller.VerticalScrollBarVisibility" Value="Hidden" />
+                        <Setter Target="scroller.VerticalScrollBarVisibility" Value="Disabled" />
                         <Setter Target="scroller.VerticalScrollMode" Value="Disabled" />
                         <Setter Target="ScrollBackBtn.Padding" Value="4,12,4,12" />
                         <Setter Target="ScrollBackBtn.Margin" Value="8,0,0,0" />
@@ -210,9 +210,9 @@
                 </VisualState>
                 <VisualState x:Name="VerticalState">
                     <VisualState.Setters>
-                        <Setter Target="scroller.HorizontalScrollBarVisibility" Value="Hidden" />
+                        <Setter Target="scroller.HorizontalScrollBarVisibility" Value="Disabled" />
                         <Setter Target="scroller.HorizontalScrollMode" Value="Disabled" />
-                        <Setter Target="scroller.VerticalScrollBarVisibility" Value="Hidden" />
+                        <Setter Target="scroller.VerticalScrollBarVisibility" Value="Disabled" />
                         <Setter Target="scroller.VerticalScrollMode" Value="Enabled" />
                         <Setter Target="ScrollBackBtn.Padding" Value="12,4,12,4" />
                         <Setter Target="ScrollBackBtn.Margin" Value="0,8,0,0" />