Allow refactorings to be previewed

[mjbvz]

Feature request

When refactoring, it should be possible to preview the refactoring in the refactor menu, similar to how we support previews of renames

[justschen]

Added an additional command in the command palette that allows users to "Refactor with preview" - viewing refactorings in the refactor preview terminal instead of immediately applying refactor changes.

Normal Refactor flow:

Refactor with Preview (similar to the renaming preview):

Moving forward, we'll be modifying the refactoring menu and potentially adding additional refactoring preview options.