Moving flag creation to a separate file

> This provides better control over proguarding descriptions
> Enforcing bug number in flag creation

Bug: 270386012
Test: Presubmit and verified on device
Change-Id: I31014e397690379024d2e42c0e913ce806b9569c
Merged-In: I31014e397690379024d2e42c0e913ce806b9569c
17 files changed