Add golden tests for systemfeatures codegen

Add a simple golden test suite for systemfeature codegen. This can be
run via atest, or as a standalone script. The golden sources can be
updated via:

  ./frameworks/base/tools/systemfeatures/tests/golden_test.sh --update

Test: atest systemfeatures-gen-golden-tests
Bug: 203143243
Flag: NA

Change-Id: Iacb9558617845132ccfffbae34c333d39c84c065