EA-109600 - NA: EditorImpl.<init>

It was an artifact of the past when GrSignature could contain several signatures at once (GrMultiSignature).

It's no longer used to compute applicability.

we can't do read action in FileContentQueue, because it can run concurrently with a write action waiting for it (at least in tests), and that would produce a deadlock

add test

This reverts commit 95046920

- skip processed classloaders when doing findResource, getResourceAsStream, findResources
- do not even try to load class with qname starting "java." or "javax."

IDEA-CR-39679 restore useful validity check (e.g. EA-125970 - assert: PsiReferenceExpressionImpl$TypeEvaluator.fun)

(Run Configurations case)

This is how it was:
tox [arguments] -e py27
It worked for all cases except
tox -- args-for-env -e py27

This is how it works now
tox -e py27 [arguments]

more speedup for DaemonRespondToChangesTest.testExpressionListsWithManyStringLiteralsHighlightingPerformance

less code, less duplication, less CPU usage

java completion: prefer 'return' if what comes after it can be parsed as a single expr statement (IDEA-195934)

to avoid multiple threads doing the same work
originally parsing was moved out of lock for IDEA-73793 which is no longer actual