Fix ShortcutGuide v2 crash when Manifests directory is missing (#48171)

## Summary

Fixes #48170 — ShortcutGuide v2 crashes on launch when the bundled
`Manifests` directory is absent from the install path.

### Root Cause

The `Assets\ShortcutGuide\Manifests\*.yml` files were never reaching the
build output directory during the CI solution-level build (`msbuild
PowerToys.slnx /t:Build -graph`). The `CopyToOutputDirectory` metadata
on `<Content>` items does not reliably copy files to a shared
`OutputPath` in this build configuration. As a result, the WiX installer
generator found no yml files to package, and the installed product was
missing the Manifests directory entirely.

At runtime, `PowerToysShortcutsPopulator.Populate()` threw an unhandled
`FileNotFoundException` causing a crash loop.

### Fix (3 layers)

1. **Code resilience** (`Program.cs`, `PowerToysShortcutsPopulator.cs`):
- Wrap `Populate()` in try/catch so a missing manifest degrades
gracefully instead of crashing
   - Add `File.Exists` guard before `File.ReadAllText`

2. **Build output** (`ShortcutGuide.Ui.csproj`):
- Add explicit `CopyManifestsToOutputDir` MSBuild target
(`AfterTargets="Build"`) that copies yml files to
`$(OutDir)Assets\ShortcutGuide\Manifests\` — same pattern as the
existing `CopyPRIFileToOutputDir` target
- Keep `<Content Include>` with `CopyToOutputDirectory` as a fallback
for publish scenarios

3. **Installer packaging** (`generateAllFileComponents.ps1`,
`ShortcutGuide.wxs`):
   - Add `*.yml` to the file inclusion list
- Add `Generate-FileList` / `Generate-FileComponents` calls for
`ShortcutGuideManifestsFiles`
- Add WiX directory definition and `RemoveFolder` component for the
Manifests directory

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>