[Xamarin.Android.Build.Tasks] property refactoring/cleanup

[jonathanpeppers]

Context: master...jonathanpeppers:fully-incremental

I am working on a revamp of the <GenerateJavaStubs/> MSBuild task to
make it "fully incremental".

The following parts of the build would happen on a per-assembly basis:

• Java sources generated
• Java class files compiled via javac
• classes.zip or *.jar files

This will be hidden behind a feature flag such as
/p:_AndroidFullyIncremental=True for its first implementation.

The problem I am facing is that our build throws random Java sources
into $(IntermediateOutputPath)android\src throughout the build. This
includes files like R.java, MonoRuntimeProvider.java, etc.

To make it where the location of these files is modifiable, we can
create a few new private properties:

• $(_AndroidIntermediateJavaSourceDirectory) which is $(IntermediateOutputPath)android\src\
• $(_AndroidIntermediateJavaClassDirectory) which is $(IntermediateOutputPath)android\bin\classes\
• $(_AndroidIntermediateClassesZip) which is $(IntermediateOutputPath)android\bin\classes.zip

This way I can modify the location when the _AndroidFullyIncremental
feature flag is set.

To refactor things a bit further, I also removed usage of
$(MonoAndroidIntermediate) and just used $(IntermediateOutputPath)
instead. $(IntermediateOutputPath) should be generally more
well-known for MSBuild, and I kept the original property around
because I found usage in other repos.

[dellis1972]

I think we have been using Path or Directory for must of our properties historically, rather than Dir, it is only a minor thing.

Also I found it seem there is a "convention" in MSBuild. Things ending with Path are relative paths, things ending with Directory are full paths. Not sure if that is official, and I'm sure we break those rules even if they are 🤷‍♂ Otherwise this looks good, it gives us options :)

  <Target Name="Foo">
    <Message Text="$(IntermediateOutputPath)" />
    <Message Text="$(MSBuildThisFileDirectory)" />
  </Target>

Foo:
  obj/Debug/
  /Users/dean/Projects/foo645539/

[jonathanpeppers]

I was looking at the list here: https://docs.microsoft.com/en-us/visualstudio/msbuild/msbuild-reserved-and-well-known-properties

There are ones one here named *Path that are full paths, like MSBuildToolsPath. Then they have others like MSBuildThisFileFullPath... Maybe no one is consistent?

I think I could just rename Dir -> Directory and that reads better.

[jonathanpeppers]

It looks like there is a change needed on the monodroid side, let me look into that.