Prepare to obsolete -warnings-as-errors in tidy_flags

* A follow up CL will set const NoWarningsAsErrorsInTidyFlags
  and make it an error to use -warnings-as-errors in tidy_flags.
* Append TidyGlobalNoChecks after local tidy_checks to disable some checks.
* Append TidyGlobalNoErrorChecks after local tidy_checks_as_errors
  (-warnings-as-errors) to allow some warnings globally.
* Move bugprone-signed-char-misuse and bugprone-branch-clone to
  globalNoErrorCheckList so we can find and fix some of those warnings.

Bug: 229801437
Test: WITH_TIDY=1 make; make tidy-soong_subset
Change-Id: I0128b859b7be6eb9bbda1916b89a6a471b052150