Merge #4270

4270: Improve derive macro completion r=edwin0cheng a=SomeoneToIgnore

* Adds completions for standard derive macros (considering their dependencies on each other, so we don't get compile errors)
* Adds completions for custom derive macros that are in scope, if the proc macro feature is enabled in the settings
* Separates macro completion from other completions to avoid incorrect completion propositions

Co-authored-by: Kirill Bulatov <mail4score@gmail.com>