Move isUntrustedActivityDefaultViewModelArgsEnabled to ActivityFlags

Renamed `enableExportedActivityDefaultArgs` to `isUntrustedActivityDefaultViewModelArgsEnabled` and moved from `ComponentActivity` to `ActivityFlags`.

Delete the `ExportedActivityDefaultArgControl` annotation, as it is no longer needed since `ActivityFlags` is covered by `ExperimentalActivityApi`.
Change `ComponentActivity.Companion` to be internal.
Update API files and tests to reflect these changes.

RelNote: N/A
Fixes: 551937289
Test: ./gradlew checkApi
Change-Id: Ife3fe0b0d48b8e08e4354f0a8ccf28f1fb45a07f