Don't use a cached union/intersection type if there is an aliasSymbol

[ghost]

It's not safe to cache the creation of a value based on only some of the inputs to that creation. This updates the code to not cache the creation of a type alias with aliasSymbol defined. (Presumably we will never create a type for the same symbol twice?)

[sandersn]

This behaviour is intended. I don't know that it's super important. It's probably even less important that

type A = { a }
type B = { b }
type T = A | B
type U = A | B
declare var t: T
declare var u: U

should also print either T or U (or A | B) for both t and u.

It's more important that:

declare var x: true | false

prints 'boolean' for the type of x

[sandersn]

@ahejlsberg can you weigh in on true | false and boolean being equivalent to type B = true | false ?

[ghost]

This change looked wrong until I realized that this is the fourth declaration of a, and the first declaration has type A1, which is the type shown here.
There is a test below showing that a variable whose only declaration is of type true | false will still print as boolean.

[ahejlsberg]

@Andy-MS @sandersn This PR doesn't look right to me. In numerous places we rely on the fact that a union of a given set of types is represented by a single object identity. Why are we trying to change this? I don't see an issue referenced here so I'm not clear on the motivation.

[ghost]

Closing in favor of #17434.