Implement LOCAL_TEST_DATA to ship data with tests

This can be used to ship source data as test artifacts next to native
tests. It works for both local builds and the test bundles using
package_modules.mk.

You just specify a file list relative to the local directory, and those
files will be copied next to the executable under
/data/nativetest*/<module>/...:

  LOCAL_MODULE := mytest
  LOCAL_TEST_DATA := data/file1 file2

  /data/nativetest/mytest/mytest
  /data/nativetest/mytest/data/file1
  /data/nativetest/mytest/file2

If the data is in another directory, you may also specify a different
prefix for the source files:

  LOCAL_TEST_DATA := external/skia:resources/f.xml

  /data/nativetest/skia_test/resources/f.xml

And there's a new convenience macro to find a list of files in this
format:

  LOCAL_TEST_DATA := $(call find-test-data-in-subdirs,external/skia,"*.xml",resources)

I'll expand this to native benchmarks and fuzz tests in a later change,
since they don't have their own module classes yet.

Bug: 30564705
Test: m -j minikin_tests; ls $OUT/data/nativetest*/minikin_tests
Test: m -j continuous_native_tests dist; zipinfo -1 out/dist/*continuous_native_tests*.zip
Change-Id: Ic76a7b62e7f567f259c4ab1510ee97d26600ba9a