* Fix assertion message when missing a code action

* Added CodeRefactoringHelpers from Cyrus

* Added 'Introduce using statement' refactoring

* xlf

* Tests for 'Introduce using statement' refactoring

* Offer refactoring on vertical selection of declaration line

* Fleshed out tests

* Enable refactoring in switch sections and for invalid embedded declarations

* Removed accidental test complexity

* Enabled introducing using statement for VB

* Stop offering 'introduce using' on VB single-line If

* Added single-line lambda tests

* Document when it is that block helpers will be used

* Remaining review fixes