Fix RS0017 warnings and enable TreatWarningsAsErrors for Release builds

[Copilot]

Summary

Fixes RS0017 warnings caused by a stale ProcessUtils.StartProcess signature in the PublicAPI.Shipped.txt files, and enables TreatWarningsAsErrors for Release builds to prevent similar regressions going forward.

Changes

1. Restore old StartProcess overload in ProcessUtils.cs:
   The old StartProcess signature (without environmentVariables parameter) was a shipped API that was inadvertently removed when environmentVariables was added to the method. Restored it as a backward-compatible overload that delegates to the new method. Suppressed RS0027 on the shim since the shipped API already declares the optional parameter.

2. Add convenience StartProcess overload in ProcessUtils.cs:
   Added a new overload that accepts environmentVariables without requiring onStarted, so callers don't need to pass a trailing null. This overload delegates to the full 6-parameter method.

3. Update PublicAPI.Unshipped.txt (both netstandard2.0 and net10.0):
   Added entries for both the 6-parameter StartProcess overload (with environmentVariables and onStarted) and the 5-parameter convenience overload (with environmentVariables only).

4. Enable TreatWarningsAsErrors for Release configuration in Directory.Build.props:
   CI will now fail on any warnings in Release builds, preventing future API tracking issues from going unnoticed.

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[Copilot]

Pull request overview

This PR addresses API analyzer (RS0017/RS0026/RS0027) warnings around ProcessUtils.StartProcess by restoring a shipped overload, adjusting the unshipped API declaration for the newer overload, updating internal call sites accordingly, and tightening build hygiene by enabling warnings-as-errors in Release builds.

Changes:

• Reintroduced the shipped ProcessUtils.StartProcess(..., onStarted = null) overload as a compatibility shim delegating to the newer overload.
• Updated PublicAPI.Unshipped.txt entries (netstandard2.0 + net10.0) to remove optional default values from the newer overload signature.
• Updated runner call sites to pass an explicit null for onStarted when calling the environment-variable overload; enabled TreatWarningsAsErrors for Release builds.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/Xamarin.Android.Tools.AndroidSdk/Runners/EmulatorRunner.cs	Updates StartProcess invocation to pass explicit onStarted: null.
src/Xamarin.Android.Tools.AndroidSdk/Runners/AvdManagerRunner.cs	Updates StartProcess invocations to pass explicit onStarted: null where unused.
src/Xamarin.Android.Tools.AndroidSdk/Runners/AdbRunner.cs	Updates multiple StartProcess invocations to pass explicit onStarted: null.
src/Xamarin.Android.Tools.AndroidSdk/PublicAPI/netstandard2.0/PublicAPI.Unshipped.txt	Adjusts unshipped API entry for the env-var overload to remove optional defaults.
src/Xamarin.Android.Tools.AndroidSdk/PublicAPI/net10.0/PublicAPI.Unshipped.txt	Same unshipped API adjustment for net10.0.
src/Xamarin.Android.Tools.AndroidSdk/ProcessUtils.cs	Restores shipped overload and defines the newer env-var overload without optional defaults.
Directory.Build.props	Enables TreatWarningsAsErrors for Release configuration builds.