Make accesses to the LogGroupsMap thread safe

There was a change of concurrent read and accesses to mLogGroups which would have caused issues.

We are also moving all reads and writes of mLogGroups out of the background worker thread to avoid out of sync accesses to the log groups leading to potential duplicate group registrations.

Flag: EXEMPT minor race-condition fix
Test: repeated runs of com.android.internal.protolog.ProtoLogTest
Bug: 423195734
Change-Id: Ic1957f7e25ff9b66683340893a5f5a3a182c85c5