See references to this issue in code.

This issue is blocked on a design decision from LDM: dotnet/csharplang#7626

• Element analysis (PR Collection expressions: analyze nullability of element assignments #70192)
• Re-inference (PR Collection expressions: method type re-inference #71214)
• Checking conversion of elements to instance Add parameter type for collection initializer types (Spread element does not emit nullability warning when converting to certain collection types #78307)
• Checking conversion of elements to extension Add parameter type for collection initializer types
• Spread analysis (PR Collection expressions: nullable analysis of spread element expression #74686)
• Checking constraints on the Create method
• Analysis of Add methods during re-inference

Relates to test plan #66418