avoid side-effectful and range-marker-polluting JavaCompletionContributor.beforeCompletion when checking postfix template applicability
check psi syncability to document before the change and not after, to avoid text inconsistencies between the two
extract DummyCachingFileSystem: put all the weirdness in one place
extract method: fill elements to before refactoring data (IDEA-119223)
IllegalArgumentException fixed; cleanup
introduce variable in injected context: allow to check handler in context before starting execution (IDEA-118788)