Add refactoring action to move members to extension

[myaumura]

Reopened after addressing review feedback and build fixes #3265 and #2484

[rintaro]

At a high level, code actions implemented in sourcekit-lsp should implement SyntaxCodeActionProvider directly.

SyntaxRefactoringCodeActionProvider is just glue code that adapts SwiftRefactor refactorings from swift-syntax to SyntaxCodeActionProvider, so new code action providers in sourcekit-lsp should generally implement SyntaxCodeActionProvider directly instead of using it.

[rintaro]

The selection is moveThis() not the entire struct Inner { ... } Can you make the result like this in this case.

struct Outer<T> {
  struct Inner {}
}

extension Outer.Inner {
   func moveThis() {}
} 

[rintaro]

At a high level, code actions implemented in sourcekit-lsp should implement SyntaxCodeActionProvider directly.

SyntaxRefactoringCodeActionProvider is just glue code that adapts SwiftRefactor refactorings from swift-syntax to SyntaxCodeActionProvider, so new code action providers in sourcekit-lsp should generally implement SyntaxCodeActionProvider directly instead of using it.

Code owners discussed about this and we concluded that using SyntaxRefactoringCodeActionProvider is fine and preferable. So please disregard this comment.