* Add ITypeSymbol.IsUnmanagedType and ITypeSymbol.IsRefLikeType

Fixes #30427 and #30426

This change simplifies our data flow analysis by removing an obsolete subclass and renaming some of the components to standardized names used in the literature on lattice data flow analysis.

Fixes #23207 

Preserve non-nullable state of a value that is going through explicit conversion to an unconstrained type parameter.

Handle unconstrained type parameters in conditional operator.

Explicitly pass NullableAnnotation value to TypeSymbolWithAnnotations.Create method.

Handle unconstrained type parameters in conditional access.

Handle unconstrained type parameters in “As” conversion operator.

Remove obsolete APIs from TypeSymbolWithAnnotations

Closes #30050.
Closes #30051.

 Adjust the way nullable annotations are represented in metadata.

Closes #30075.
Closes #30065.
Closes #29594.
Closes #29683
Closes #29662

A pointer type can match a var pattern (e.g. `var x`), a discard pattern (e.g. `_`), and a constant pattern with the value null (e.g. `null`). No other pattern forms would permit an input of a pointer type.
Fixes #30798

Add tests to demonstrate that they are associative and commutative.
Add (skipped) tests to demonstrate that we have inconsistent meet and join functions.
    We will have to decide how to handle the differences.
I have not yet extracted the NullableState operations from ConversionsBase
    (e.g. testing if one NullableState is higher or lower than another in the lattice)
Also removed some inoperative code in MethodTypeInference

Fixes #30561

Remove NonNullTypes context and other unnecessary information stored in TypeSymbolWithAnnotations. (#30913)

Remove NonNullTypes context and other unnecessary information stored in TypeSymbolWithAnnotations.

Fixes #30845.

Explicitly handle nullability analysis for unconstraint type parameters.

Related to #29981, #29993

Generates fake indexers for arrays that take System.Index and
System.Range.