Support data properties for test binaries

Allow tests to specify a data property that lists files or filegroup
modules that will be packaged alongside the test.  Also add a path
property to filegroup modules to allow shifting the path of the
packaged files, and add ExpandSourcesSubDir to expand the filegroup
sources while including a shifted relative path in the Paths objects.

Test: soong tests, manually adding data to a module
Change-Id: I52a48942660e12755d313ef13279313361b4fc35

Android.bp

@@ -145,6 +145,7 @@ bootstrap_go_package {
     ],
     testSrcs: [
         "cc/cc_test.go",
+        "cc/test_data_test.go",
     ],
     pluginFor: ["soong_build"],
 }