[Proposal]: Method group natural type improvements (VS 17.9, .NET 9)

# Method group natural type improvements

* [x] Proposed
* [ ] Prototype: Started
* [ ] Implementation: Started
* [ ] Specification: Not Started

## Summary
[summary]: #summary

The proposal is that the natural/weak type of a method group should be determined by looking scope-by-scope and pruning inapplicable candidates as soon as possible, instead of considering all scopes at once and letting those inapplicable candidates fail the determination process.

## Motivation
[motivation]: #motivation

The motivation for the scope-by-scope approach is to prepare a better foundation for the extension types work.
The motivation for the early pruning approach is to better align with the principle used in overload resolution.

## Detailed design
[design]: #detailed-design

See https://github.com/dotnet/csharplang/blob/main/proposals/method-group-natural-type-improvements.md

## Design meetings

- LDM 8/7
- https://github.com/dotnet/csharplang/blob/main/meetings/2023/LDM-2023-07-24.md