Sort Rust TEST_MAPPING tests.

We currently seem to emit TEST_MAPPING files in an arbitrary order,
which causes diffs to look confusing even when nothing has changed.
Let's sort them by the test name, which is both stable and easier to
read.

Test: Run cargo2android multiple times and see no TEST_MAPPING diff.
Change-Id: I398aa84a4891380e4292223445bd53959c024421
1 file changed