Extract snippet from file `refactor.extract` CodeAction

The LSP defines some CodeActionKinds that have special meanings in some Language Clients. One of those is the RefactorExtract action kind.

We could probably offer a RefactorExtract action when you highlight a large range of text inside a section|template|snippet.

When executed, we could do something like this:

• For range Y in input file X:
  1. Find all non-global variables in Y
  2. Create a file snippets/Z.liquid with the contents of Y
  3. Replace Y in X by the following:

    {%
      render '#{Z}',
      #{all_the_non_global_variables_as_arguments}
    %}
  

To be answered:

• Can we prompt for a filename during that process?

Resources

1. https://microsoft.github.io/language-server-protocol/specifications/specification-3-17/#textDocument_codeAction

Start with the proposed behavior in this issue and read the linked LSP CodeAction specification. Identify the language-server entry point for CodeActions and determine how range variables, snippet creation, replacement text, and filename prompting should work. Done means a RefactorExtract action can perform the described extraction with a clear filename flow.