Reserve .rs extension for Rust.
Bug: 137365032
Test: make checkbuild
Test: cd frameworks/compile/slang/tests
./slang_tests.py
Test: atest CtsRenderscriptTestCases
Test: CtsRsCppTestCases
Exempt-From-Owner-Approval: Clean CP
Change-Id: Iab077f256ff3776495302606572f384d82ab171f
Merged-In: Iab077f256ff3776495302606572f384d82ab171f
(cherry picked from commit 4a8876ec9e)