After-review optimisation

give some unexpected background threads (like "Zip Handle Janitor") more time to finish to avoid leaks

Currently, all save sessions save() called under ONE write action, so, it is important to make sure that save() actually does ONLY flush on disk and nothing more

let FrozenDocument.lineSet be gc-able to decrease memory pressure when somebody holds too many of them (IDEA-205347)

async console highlighter: don't hold references to frozen documents after they've been processed (IDEA-205347)

save credentials on configurable's commit

[groovy] tests: split RepositoryProjectDescriptor into TestLibrary and LibraryLightProjectDescriptor

Inspection does not register `CompatibilityVisitor` problems for its opened file language because in such a case
`UnsupportedFeatures` will annotate them.
Also `registerOnFirstMatchingVersion` methods were removed because
they could lead to duplication even if languages to register were different.

Although `TestPlan` exposes an `add(TestIdentifier)` method, it was only
ever intended for internal use by JUnit's `DefaultLauncher` which
already adds dynamic test identifiers to the `TestPlan`. The JUnit team
is going to make the `add()` throw an exception on modifications from
listeners. Thus, this commit removes the unnecessary call.