* Fix UI freeze due to extract to local computations

- fixes #1185
- don't run checkFinalConditions() from QuickAssistProcessor to see if
  extract to local variable proposals are valid
- override the preview for extract to local variable and extract to
  local variable (replace all occurrences) so they just display a
  message instead of creating the change
- fix ExtractTempRefactoring.checkFinalConditions() to recognize an
  invalid change in which case add a fatal error status with a code from
  RefactoringStatusCodes
- modify RefactoringCorrectionProposalCore to recognize the
  error and create a dummy edit plus a log entry to note that
  the extraction will not occur
- fix AssistQuickFixTest tests proposal counts