Experimental feature: LOCAL_PATCH_MODULE option in .mk files.

Specifying this option causes the make target's sources
and classpath dependencies to be patched into the specified
module via --patch-module (if the build toolchain implements
the module system, ie. when targeting 1.9). This allows tests
to compile that have classes in packages under test.

Currently, only java.base is on the module path (everything
else is on the classpath), and only when using -target 1.9
(ie. EXPERIMENTAL_USE_OPENJDK9=true).

Bug: 71699916
Test: Treehugger
Test: Checked that I was able to compile some ojluni & icu
      test sources that had classes in (libcore) packages
      under test.

Change-Id: I044fb9d904754ed281f574ab3dd52235cf0d7fec