Fix watch mode errors on scope changes after transpilation

[luis-j-soares]

This PR attempts to fix a watch mode issue where field initialisers will trigger diagnostic errors after their scope is transpiled.

Notes:

• This is still a draft because fixing this with .clone() breaks enums. Still figuring out how to fix that.
• Reverted the .clone() solution because it conflicts with how the transpile method of enum/const value expressions are overwritten by editor. It might be better to clone the entire AST before transpiling the file, but that might incur its own issues...
  • Cloning the AST of a file could significantly increase memory usage;
  • The AST would need to be walked all over again to set parent references, which delays transpiling times;
  • Any plugin logic that stores AST node references on parse/validate will break, as transpile methods would effectively be working with a different AST.

[luis-j-soares]

Closing this as I can't find a solution, and it's likely better to focus on this for the v1 branch. Opened #1613 instead so we can track it.