[build] Default .NET 11 to target net11.0-android37 only

[jonathanpeppers]

Stop building API 36.1 as a separate stable target and make net11.0-android37 the sole default target framework for .NET 11.

Changes:

• Configuration.props: Set AndroidLatestStableApiLevel to 37, AndroidLatestStablePlatformId to 37.0 (explicit, since Google ships platform-37.0), framework version to v17.0. Unstable properties now reference stable (since they are the same). Updated AndroidLatestStableApiLevel2 comment example to 38.1.
• AndroidToolchain.cs: Move isLatestStable from platform-36.1 to platform-37.0, remove isPreview flag
• WorkloadManifest.in.json: Update workload packs from 36.1 to 37, add Mono/CoreCLR/NativeAOT runtime pack definitions for 37, remove 36.1 pack definitions
• Xamarin.Android.Build.Tasks.targets: Use $(AndroidLatestStablePlatformId) for @SDK_PLATFORM_VERSION@ replacement instead of $(AndroidLatestStableApiLevel) (needed because ApiLevel=37 but PlatformId=37.0)
• BuildTest.cs: Hardcode MinorApiLevelFallbackThrowsXA5207 to use 36.1 since 37.0 == 37 (no meaningful minor version distinction for this test scenario)

Note: AndroidLatestStablePlatformId is now explicitly set to 37.0 rather than defaulting to $(AndroidLatestStableApiLevel). This is because Google ships the platform as platform-37.0 (directory android-37.0), but the API level for TFMs and PublicAPI directories is just 37. Previous APIs (like 36 and 36.1) happened to have identical ApiLevel and PlatformId values.