Add lightbulb refactor helper to move code to an existing file

[mekwall]

I would like to see a lightbulb refactor helper similar to the "Move to a new file" helper but instead move it to an existing file in the code base.

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• Manually triggered code actions can replace lightbulb actions (#88485)

[mjbvz]

Duplicate of microsoft/TypeScript#29988