Support 'refactor.extract.function' refactoring

[ktoso]

Describe the solution you'd like
A common refactoring task is to take a selection and extract it into a method, currently this is not supported by this plugin:

Additional context
This is a common refactoring and we should support it in the Swift plugin.

[award999]

@ktoso there is an extract method code action, is that what you are looking for?