Ensure singleton types always compare identical

[ahejlsberg]

This PR ensures the "singleton" types (any, unknown, string, number, boolean, bigint, symbol, void, undefined, never, and object) always compare identical when their type kind matches, regardless of type object identity. This in particular ensures that the undefined used to represent a missing property compares identical to the "regular" undefined.

The PR also ensures that TypeFlags.Boolean is consistently set on any union of the boolean literal values true and false. We weren't setting this flag on type alias declarations for true | false.

Fixes #44388.

[weswigham]

A testcase for the BooleanLiteral parts of this change (so we avoid regressing) would be nice.

[awerlogus]

Will this also fix #44453?

[ahejlsberg]

@weswigham Except for error messages in one case (for an indexed access type [number][boolean] where we just report an error for boolean instead of true and false separately) we have no compiler behaviors that change based on whether TypeFlags.Boolean is set or not, so adding a test isn't super useful. My main concern was external dependencies such as linters.