Proposal: more improvements to nullable reference types

[jcouv]

Follow-up on C# 9 work.

Considered for C# 10:

• Task<T> (LDM tentatively approved, needs design proposal for task-like types)
• LINQ (LDM expressed interested to handle Where, needs design proposal)
• uninitialized fields and constructors (no plan, aside from MemberNotNull)

[alrz]

uninitialized fields and constructors

I understand this isn't about records but could that replace #3630 somehow?

I think the important distinction is to warn on object construction (new) rather than inside the constructor.

[jcouv]

Closing in favor of #3950 (Task) and #3951 (LINQ).
The discussion of initialization debt is covered by required properties feature.