(cherry picked from commit 259542b)

We now properly strip trailing whitespace. Add in spacing after `{` and
before `}`.

(cherry picked from commit 195823b)

This was called `SourceEdit`, which would be nice to reserve for
refactorings rather than incremental parsing. Ideally we'd also move all
the incremental parsing types into `SwiftParser` as well.

(cherry picked from commit 40f2954)

This adds an additional text-based refactoring provider which the
original syntax-based provider now implements. This allows refactorings
that produce text rather than a full tree.

(cherry picked from commit bcf0d1f)

Adds three new refactorings:
  - `ConvertToTrailingClosures`
  - `ExpandEditorPlaceholder`
  - `ExpandEditorPlaceholders`

`ExpandEditorPlaceholders` is a combination of `ExpandEditorPlaceholder`
and `ConvertToTrailingClosures`, ie. it first expands any function-typed
closures at the end of a call using `ExpandEditorPlaceholder` and then
runs `ConvertToTrailingClosures` on that call.

Resolves rdar://107532856.

(cherry picked from commit c70e54a)