feat: add multiple getters mode in `generate_getter`
This commit adds two modes to generate_getter action.
First, the plain old working on single fields.
Second, working on a selected range of fields.
Should partially solve #13246
If this gets approved will create a separate PR for setters version of the same
### Points to help in review:
- `generate_getter_from_record_info` contains code which is mostly taken from assist before refactor
- Same goes for `parse_record_fields`
- There are changes in other assists, as one of the methods in utils named `find_struct_impl` is changed, before it used to accept a single `fn_name`, now it takes a list of function names to check against. All old impls are updated to create a small list to pass their single element.
### Assumptions:
- If any of the fields have an implementation, the action will quit.
f3cce5feea