Use output file arg for systemfeatures-lookup-gen tool

Prefer using an explicit output file as the target for generated code,
rather than piping from stdout. This avoids issues with spurious JDK
stdout logs leaking into the generated source file.

Bug: 421912364
Test: atest systemfeatures-gen-tests
Flag: EXEMPT trivial tooling bug fix
Change-Id: Ic70caf6fd123e77458c0ba27889617129378e309