Describe V9 branches and PRs

[BillWagner]

Updates notes for V9 feature branches and new draft PRs for V9 features:

• Init accessors
• Top level statements
• native-sized integers
• records
• function pointers
• v9 patterns
• static anonymous functions
• target-typed conditional expressions
• covariant return types
• Extension GetEnumerator support
• lambda discard parameters
• attributes and extern on local functions
• Module initializers
• partial method updates
• target-typed new
• Unconstrained type parameter annotation
• Variance safety for static interface members
• Nullable reference type updates (better static analysis, default constraint)

[BillWagner]

The PR for target-typed conditional expressions (#1071) seems corrupt. Skipping that one for now.

[BillWagner]

Also, skipping covariant return types, as there isn't a draft PR yet.

[RexJaeschke]

@BillWagner I just created Draft PR #1462 for covariant return types and checked that box in this PR's feature tracking list.

[RexJaeschke]

@BillWagner I just created Draft PR #1465 for (the previously damaged) target-type conditional expressions feature spec and checked that box in this PR's feature tracking list.

[BillWagner]

@RexJaeschke

This is ready for review and merging. All the V9 PRs are in feature branches.

[RexJaeschke]

@BillWagner I still have 4 of these to review, but I agree that you have moved all those that needed moving (including 1221, nullable attributes held over from v8). So I'll approve this PR. That said, I do have some questions about seemingly odd things that happened during the move in at least 2 of those remaining 4, but I'll get back to you on those separately.

Separately, the following specs are in the MS v9 proposals folder, and for which I have not created a PR:

1. https://github.com/dotnet/csharplang/blob/main/proposals/csharp-9.0/skip-localsinit.md
2. https://github.com/dotnet/csharplang/blob/main/proposals/csharp-9.0/nullable-constructor-analysis.md
3. https://github.com/dotnet/csharplang/blob/main/proposals/csharp-9.0/nullable-parameter-default-value-analysis.md

As I noted in their corresponding entries in the GitHub v9 feature tracker, as far as I can tell, these are compiler/implementation issues and need no text in the language spec. Please look at them to see if that is correct.

[RexJaeschke]

@Bill I made corrections to 2 PR number links, and once you confirm those are correct I can approve this.

[BillWagner]

Thanks @RexJaeschke Those corrections are correct.