patch_sdk tool must return non-zero error code if it reported any nits/warnings/errors #30127
Description
E.g.:
[4737/17343] ACTION //flutter/lib/snapshot:flutter_patched_sdk(//build/toolchain/fuchsia:x64)
Not enabling colors, stdout does not support ANSI colors.
flutter_patched_sdk/lib/ui/ui.dart: Nit: 'Symbol' is imported from both 'dart:_internal' and 'dart:core'.
See GN guidelines here: https://github.com/dart-lang/sdk/wiki/Building-with-GN#hints-suggestions-etc
In particular: "A successful GN build produces no output."
/cc @sigmundch