Preferred refactorings

[mjbvz]

Problems

• Refactorings such as extract function and extract constant may return multiple possible locations where the code could be extracted to. In many cases however, the user would just like to quick extract something to a reliable location and continue on.

• extract function is always returned alongside extract constant. However it is often desirable to extract to a constant instead of a function when possible.

Proposal In the TS Server protocol, mark some refactoring as a preferred refactorings. Editors could use this information to automatically select the preferred refactoring in the list or even quick apply it without any user input (see https://github.com/Microsoft/vscode/issues/62110 for VS Code's proposal on this)

Preferred refactorings would let users set up actions such as extract constant that reliably extract to the nearest scope with a single action or keyboard shortcut. The UX behavior for this type of action:

• If only a single isPreferred refactoring is returned, apply it automatically.

• If multiple preferred refactorings are returned, show a list of the preferred refactorings that the user can select from

The normal refactor context menu with full list of refactorings would continue to display the full list of refactorings.

We can start conservative with which refactorings are preferred:

• For extract constant, extract to local const
• For extract function, extract to function at the scope of the parent function
• For extract function in a method, extract to a method

Related to a similar proposal for quick fixes #29450

[mjbvz]

Marking as a priority since this is a smaller feature that would better align TS with the LSP