Improve sig info, error message formatting when working with complex generic code

[tmat]

Working with types that combine generics and tuples is cumbersome. The IDE does not help much at all.

using var _ = PooledDictionary<string, ArrayBuilder<(ManagedActiveStatementDebugInfo info, SourceFileSpan span, int ordinal)>>.GetInstance(out var updatedSpansByDocumentPath);

var x = updatedSpansByDocumentPath.ToImmutableDictionary(
     keySelector: 

Can we structure the signatures better using line breaks and indentation?

Sig info:

Hover:

Types in diagnostic not colorized and the error is hard to read with the long type names in the middle of the error message:

[Youssef1313]

Related to #29949 and #33609.

[jinujoseph]

Need a proposal before bringing to design meeting

[DoctorKrolic]

@CyrusNajmabadi You fixed this issue in #56025, so it should be closed now

[CyrusNajmabadi]

Works for me. Thanks!