Merge #9614

9614: Parse input expressions for dbg! invocations in remove_dbg r=Veykril a=Veykril

Instead of inspecting the input tokentree manually, parse the input as `,` delimited expressions instead and act on that. This simplifies the assist quite a bit.

Fixes #8455

Co-authored-by: Lukas Wirth <[email protected]>

Author: bors[bot]