Context: dotnet/android#10438

9 months ago in [The First Developer Preview of Android 16][0]:

> **Two Android API releases in 2025**
>
>   * This preview is for the next major release of Android with a
>     planned launch in Q2 of 2025. This release is similar to all of
>     our API releases in the past, where we can have planned
>     behavior changes that are often tied to a targetSdkVersion.
>
>   * …
>
>   * We plan to have another release in Q4 of 2025 which also will
>     include new developer APIs. The Q2 major release will be the
>     only release in 2025 to include planned behavior changes that
>     could affect apps.

The 3rd bullet point is a "25Q4 MINOR SDK RELEASE" , thus introducing
the *concept* of a "minor" SDK version, with semantics:

  * [`<uses-sdk/>`][3]:

    > It's not possible to specify that an app either targets or
    > requires a minor SDK version.

  * [Using new APIs with major and minor releases][4]:

    > The new [`SDK_INT_FULL`][5] constant can be used for API checks…
    >
    >     if (SDK_INT_FULL >= VERSION_CODES_FULL.[MAJOR or MINOR RELEASE]) {
    >       // Use APIs introduced in a major or minor release
    >     }
    >
    > You can also use the [`Build.getMinorSdkVersion()`][6] method to
    > get just the minor SDK version:
    >
    >     minorSdkVersion = Build.getMinorSdkVersion(Build.VERSION_CODES_FULL.BAKLAVA);

Update `AndroidVersion` and `AndroidVersions` to better support the
concept of "minor SDK releases":

  * Add a new `AndroidVersion.VersionCodeFull` property, which is a
    `System.Version` -- not an `int` -- for which `Version.Major`
    matches `AndroidVersion.ApiLevel`.

  * Add a new internal `AndroidVersion.Ids` property, which is the=
    full set of "aliases" that should be checked when doing an "id"
    match.  This simplifies `AndroidVersions` logic.

    `Ids` contains: `ApiLevel`, VersionCodeFull`, and `Id`.

  * Change `AndroidVersions.AlternateIds` into a set-only property
    which updates `AndroidVersion.Ids`.

  * Bump `$(LangVersion)`=9.0 to use target-typed `new()`.

[0]: https://android-developers.googleblog.com/2024/11/the-first-developer-preview-android16.html
[3]: https://developer.android.com/guide/topics/manifest/uses-sdk-element
[4]: https://developer.android.com/about/versions/16/features#using-new
[5]: https://developer.android.com/reference/android/os/Build.VERSION#SDK_INT_FULL
[6]: https://developer.android.com/reference/android/os/Build#getMinorSdkVersion(int)