Add crunch-flags and build-flag binaries

- crunch-flags automates converting build flags from starlark to protobuf.
- build-flag is used to set, get and trace flag values.

Bug: 328495189
Test: manual
Ignore-AOSP-First: cherry-pick
Merged-In: I941a4420a8bdfa2df73d94e52b3f34a6d1ea3278
Change-Id: I941a4420a8bdfa2df73d94e52b3f34a6d1ea3278