Restrict InspectClass to current thread.

If there are other threads asking for class restransformation
InspectClass may be called during the transient period of time when the
callback is enabled. More importantly InspectClass could be called after
jvmti env is disposed, which would lead to native crashes.

Bug: 121234522
Test: Manual tests. dexmaker-extended-mockmaker-tests passed.
Change-Id: Ic62951ff81bed60ac7512455fad65210e4b728a9