Merge EnforcePermissionHelperDetector with EnforcePermissionDetector

Both classes shared similar code. The main merging is between
visitAnnotation and visitMethod. The tests are not modified beyond what
is strictly necessary. This ensures that this refactoring does not break
existing functionality.

Bug: 260314719
Test: atest --host AndroidGlobalLintCheckerTest
Test: atest --host AndroidGlobalLintCheckerIntegrationTest
Change-Id: I6d09d311f6d8bee88ea2b2d2cd4e647d941d9979