[Xamarin.Android.Build.Tasks] fix bug in AndroidFastDeploymentType=Assemblies::Dexes

The app at runtime in the `ApplicationRunsWithDebuggerAndBreaks` test
was crashing at runtime with:

    01-16 13:11:42.395  4273  4273 E monodroid-assembly: typemap: failed to stat TypeMap index file '/data/user/0/com.xamarin.applicationrunswithdebuggerandbreaks/files/.__override__/typemaps/typemap.index': No such file or directory
    01-16 13:11:42.395  4273  4273 F monodroid-assembly: typemap: unable to load TypeMap data index from '/data/user/0/com.xamarin.applicationrunswithdebuggerandbreaks/files/.__override__/typemaps/typemap.index'

This only happens when `AndroidFastDeploymentType=Assemblies::Dexes` is
used, as it is the case when typemap files like this are fast deployed
and used at runtime.

What was even more odd, was the file seems to exist after a
`-t:Install`, but ends up missing after `-t:Run`:

    > adb shell run-as com.xamarin.applicationrunswithdebuggerandbreaks ls -la files/.__override__/typemaps/typemap.index
    ls: files/.__override__/typemaps/typemap.index: No such file or directory

It appears that `-t:Install` successfully deploys the file:

    Pushed 3969 to /data/local/tmp/.xatools/typemap.index
    DEBUG RunShellCommand emulator-5554 "run-as" "com.xamarin.applicationrunswithdebuggerandbreaks" "--user" "0" "files/.__tools__/xamarin.cp" "/data/local/tmp/.xatools/typemap.index" "files/.__override__/typemaps/typemap.index" "1705432079367" [5ms]
    files/.__tools__/xamarin.cp returned: moved [/data/local/tmp/.xatools/typemap.index] to [files/.__override__/typemaps/typemap.index] modifieddate [1705432079367]
    moved /data/local/tmp/.xatools/typemap.index to files/.__override__/typemaps/typemap.index
    Installed files/.__override__/typemaps/typemap.index. [12ms]
    NotifySync CopyFile obj\Debug\android\typemaps\typemap.index. [0ms]

But then `-t:Run` deletes the file!

    Remove redundant file files/.__override__/typemaps/typemap.index
    DEBUG RunShellCommand 0A041FDD400327 "run-as" "com.xamarin.applicationrunswithdebuggerandbreaks" "rm" "-Rf" "files/.__override__/typemaps/typemap.index" [29ms]

This happens because the `@(_AndroidTypeMapping)` item group is empty
during an incremental build:

* The `<GenerateJavaStubs/>` MSBuild task, during the first build
  outputs `@(_AndroidTypeMapping)` items

* During an incremental build, the `_GenerateJavaStubs` MSBuild *target*
  is skipped, and so the `@(_AndroidTypeMapping)` item group is empty!

* The `<FastDeploy/>` task happily deletes files that it thinks should
  be removed.

For now, let's add logic to the `_GenerateJavaStubs` target to fill in
the `@(_AndroidTypeMapping)` item group during incremental builds:

  <ItemGroup Condition=" '$(_InstantRunEnabled)' == 'True' and '@(_AndroidTypeMapping->Count())' == '0' ">
    <_AndroidTypeMapping Include="$(_NativeAssemblySourceDir)typemaps\*" />
  </ItemGroup>

`<ItemGroup>`s are still evaluated when a target is *skipped*, solving
the problem.

I assume this is working in `main`, because Xamarin.AndroidX.Migration
package was involved. It likely was running the `_GenerateJavaStubs`
target on every build. Will verify.

Author: jonathanpeppers

src/Xamarin.Android.Build.Tasks/Xamarin.Android.Common.targets

@@ -1542,6 +1542,10 @@ because xbuild doesn't support framework reference assemblies.
     <Output TaskParameter="GeneratedBinaryTypeMaps" ItemName="_AndroidTypeMapping" Condition=" '$(_InstantRunEnabled)' == 'True' " />
   </GenerateJavaStubs>
 
+  <ItemGroup Condition=" '$(_InstantRunEnabled)' == 'True' and '@(_AndroidTypeMapping->Count())' == '0' ">
+    <_AndroidTypeMapping Include="$(_NativeAssemblySourceDir)typemaps\*" />
+  </ItemGroup>
+
   <ItemGroup>
     <FileWrites Include="@(_TypeMapAssemblySource)" />
     <FileWrites Include="@(_TypeMapAssemblyInclude)" />