[Mono.Android] Bind API-VanillaIceCream Beta 1 (#8891)

[Mono.Android] Bind API-VanillaIceCream Developer Preview 2

Context: https://developer.android.com/about/versions/15
Context: https://android-developers.googleblog.com/2024/04/the-first-beta-of-android-15.html
Context: 00256b6

Android 15 Beta 1 has been released on 2024-Apr-11:

  * [API-VanillaIceCream Beta 1 vs. API-34][1]
  * [API-VanillaIceCream Beta 1 vs. Developer Preview 2][2] (00256b6)

The Android 15 Developer Preview [Timeline and updates][3] section
suggests the following timeline, unchanged from 00256b6:

  * Feb/Mar: Developer Previews
  * April/May: Unstable Betas
  * June/July: Stable Betas with a [Platform Stability milestone][4]
    expected in Beta 3.
  * ???: Final

This will be usable in its preview form to .NET 9 Preview 4+ users
who explicitly target `net9.0-android35`.

~~ Acceptable Breakages ~~

`PublicApiAnalyzers` reports 1 API change in `PublicAPI.Shipped.txt`:

	- virtual Android.App.Admin.DevicePolicyManager.GetPendingSystemUpdate(Android.Content.ComponentName! admin) -> Android.App.Admin.SystemUpdateInfo?
	+ virtual Android.App.Admin.DevicePolicyManager.GetPendingSystemUpdate(Android.Content.ComponentName? admin) -> Android.App.Admin.SystemUpdateInfo?

We deem this acceptable as:

 1. It isn't an ABI break, and
 2. For *callers* of `GetPendingSystemUpdate()`, this shouldn't be an
    API break, as the "domain" of valid parameters "expands" to
    accept `null`.  However-
 3. For *overriders* of `GetPendingSystemUpdate()`, this *could* be
    an API break, as they would not be expecting `null`.
    However, we feel that this method is unlikely to be overridden
    *other than in binding code*, so we'll hand-wave it away.

[0]: https://android-developers.googleblog.com/2024/04/the-first-beta-of-android-15.html
[1]: https://developer.android.com/sdk/api_diff/v-beta1/changes
[2]: https://developer.android.com/sdk/api_diff/v-beta1-incr/changes
[3]: https://web.archive.org/web/20240418175822/https://developer.android.com/about/versions/15/overview#timeline
[4]: https://web.archive.org/web/20240418175822/https://developer.android.com/about/versions/15/overview#platform_stability

build-tools/xaprepare/xaprepare/ConfigAndData/Dependencies/AndroidToolchain.cs

@@ -71,7 +71,7 @@ public AndroidToolchain ()
 				new AndroidPlatformComponent ("platform-32_r01",   apiLevel: "32", pkgRevision: "1"),
 				new AndroidPlatformComponent ("platform-33-ext3_r03",   apiLevel: "33", pkgRevision: "3"),
 				new AndroidPlatformComponent ("platform-34-ext7_r02",   apiLevel: "34", pkgRevision: "2", isLatestStable: true),
-				new AndroidPlatformComponent ("platform-VanillaIceCream_r02",   apiLevel: "VanillaIceCream", pkgRevision: "2", isLatestStable: true),
+				new AndroidPlatformComponent ("platform-VanillaIceCream_r03",   apiLevel: "VanillaIceCream", pkgRevision: "3", isLatestStable: true),
 
 				new AndroidToolchainComponent ("sources-34_r01",
 					destDir: Path.Combine ("sources", "android-34"),