[Java.Interop-MonoAndroid.csproj] Add ProjectReference to 'jnienv-gen'.

[jpobst]

Fixes a parallel build issue in Xamarin.Android by adding a project reference to jnienv-gen.csproj from Java.Interop-MonoAndroid.csproj. This ensures jnienv-gen.exe is available when building Java.Interop-MonoAndroid.csproj.

Java.Interop-MonoAndroid.csproj is built via the <MSBuild> task and was previously called with global properties specifying MonoAndroid1.0 target framework.

    <PropertyGroup>
      <_GlobalProperties>
        JavaInteropProfile=Net45;
        XAInstallPrefix=$(XAInstallPrefix);
        TargetFrameworkIdentifier=MonoAndroid;
        TargetFrameworkVersion=v1.0;
        TargetFrameworkRootPath=$(XAInstallPrefix)xbuild-frameworks;
      </_GlobalProperties>
    </PropertyGroup>
    <MSBuild
        Projects="$(JavaInteropFullPath)\src\Java.Interop\Java.Interop-MonoAndroid.csproj"
        Properties="$(_GlobalProperties)"
    />

However these properties flow to the jnienv-gen build, causing it to build as monoandroid10 instead of net472.

Move the TargetFramework* global properties from Mono.Android.targets to regular properties in Java.Interop-MonoAndroid.csproj so they are not passed to jnienv-gen.csproj.

This project will now be called with:

      <_GlobalProperties>
        JavaInteropProfile=Net45;
        XAInstallPrefix=$(XAInstallPrefix);
      </_GlobalProperties>

XA Companion PR: dotnet/android#7068