[ci] Pin test slicer to repo-local runtime (#12706)

## Why

Hosted macOS builds [1574631](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1574631) and [1574989](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1574989) installed `dotnet-test-slicer` successfully, then failed before running tests because its native apphost could not locate .NET. The tool was invoked by absolute path, so adding its directory to `PATH` did not help runtime discovery; both `DOTNET_ROOT_X64` and `DOTNET_ROOT` were unset.

The pinned slicer package targets `net8.0` with `rollForward: LatestMajor`, while test setup already installs the repository-pinned compatible SDK under `bin/$(XA.Build.Configuration)/dotnet`.

Tracked by #12704.

## What changed

- Set `DOTNET_ROOT` to the repo-local SDK for every initial and retry slicer invocation.
- Forward `xaSourcePath` through the emulator-stage template so custom checkout paths resolve the same SDK installed during setup.

## Validation

- Parsed both changed YAML templates and checked parameter substitution for a custom source root.
- Confirmed all three slicer invocations receive the expanded repo-local `DOTNET_ROOT`.
- Launched `dotnet-test-slicer` 0.1.0-alpha7 successfully against a .NET 11-only runtime root, exercising its configured major-version roll-forward.

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

Localized file check-in by OneLocBuild Task (#11244)

Build definition ID 17928: Build ID 13967215

[Mono.Android] Bind API-37 Beta 3 (#11038)

Context: https://developer.android.com/about/versions/17
Context: https://android-developers.googleblog.com/2026/03/the-third-beta-of-android-17.html

Android 17 Beta 3 has been released.

  * [API-37 Beta 3 vs. API-CinnamonBun Beta 2][0]
  * [API-37 Beta 3 vs. API-36.1][1]

The Android 17 Beta 3 announcement states that Beta 3 is API stable.

> Android 17 has officially reached platform stability today with
> Beta 3. That means that the API surface is locked; you can perform
> final compatibility testing and push your Android 17-targeted apps
> to the Play Store.

We're not yet ready to do the enumification work, though.

Bind API-37 Beta 3 as an *unstable*, *un-enumified* binding.

[0]: https://developer.android.com/sdk/api_diff/37-incr/changes
[1]: https://developer.android.com/sdk/api_diff/37/changes