feat: refactoring action to extract an eel statement

[PRGfx]

Introduces a new assignment for a selected part of an EEL assignment:
The selected expressions from an assignment are added to a new assignment in the preceding line and replaced with a reference to the new key. The new key can than be renamed.

ToDo/Nice-to-have:

• Implement tests
• Fix extraction for partial expressions (For most cases it should work, but there probably are some more edge-cases where a selection doesn't look like it can't be extracted - and maybe rightfully so...)
• Implement selection of scope (this, props, private) (I was thinking about a selection like var/const/let selection for JS, but this doesn't work well for me and I haven't looked into that yet.)
• Implement clean renaming of introduced variable (Currently I just place carets and selection over the new variable to allow typing over it. Full renaming logic for fusion is a bit more involved I'm afraid.)
• (Warn if new name is already in use)

The code for extracting the EEL expressions feels super scuffed, but I didn't have a nice idea for now.