Deprecate and remove ProcessStateRecord.mAllowStartFgsState field.

Its functionality can be fully covered by mCurProcState.

Also dump allowStartForeground in human-readable string.

Bug: NA.
Test: atest cts/tests/app/src/android/app/cts/ActivityManagerFgsBgStartTest.java
Change-Id: Ib76185f5a93ac37bd902a719ed7a347d85fecfde