Reserve .rs extension for Rust.

Update test results to expect the new extension.

Bug: 137365032
Test: make checkbuild
Test: cd frameworks/compile/slang/tests
    ./slang_tests.py
Test: atest CtsRenderscriptTestCases
Test: CtsRsCppTestCases

Change-Id: I53417fc10c589a845e1cefe8d41f71f8a8de1097