Renderscript: rename .rs extension to .rscript

Reserve .rs extension for Rust.

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

Change-Id: I8fc67c3569c75df4a19b609190b92938bc4c63f9
Merged-In: I8fc67c3569c75df4a19b609190b92938bc4c63f9
470 files changed