[ConstraintSystem] Rename getFixedType/assignFixedType/getFixedTypeRecursive.

[rudkx]

A few renames:

• getFixedType => getBoundType
• assignedFixedType => assignBoundType
• getFixedTypeRecursive => resolveTypeVariable

Note this PR also has all of #18325.

[rudkx]

@DougGregor @xedin Thoughts on the renames here?

getFixedTypeRecursive in particular has always bothered me since it doesn't just do getFixedType recursively, and isn't even recursive at this point.

[rudkx]

@swift-ci Please smoke test

[xedin]

{get, assign}BoundType - {get, assign}Type, because it retrieves or assigns/binds a type for/to a type variable, and resolveTypeVariable - resolveType because it could resolve/simplify multiple type variables?

[rudkx]

@xedin I had considered {get, assign}Type, but getType is already in use on ConstraintSystem and I didn't want to overload it for that purpose.

I started looking at this because I have other changes where I ended up calling getFixedType() instead of getFixedTypeRecursive() and that's an easy mistake to make. The former is just grabbing whatever type was assigned via assignFixedType(), i.e. the one bound to the type variable, whereas the latter drills down into dependent members and nested type variables, ultimately getting you to the most specific concrete type we can resolve to.

I'm not convinced resolveType() would be more clear than resolveTypeVariable(). They both have the very generic term resolve, which I'm not thrilled with but it attempts to convey the idea that we're doing something more than just a lookup.

[rudkx]

@swift-ci Please smoke test

[xedin]

The reason why I want to drop Bound is because I don't think it carries any meaning, as soon as you want to assign a type or get a type for something it has to be a "bound" type, right?

Re: getFixedTypeRecursive maybe we should change it to resolveTypeVariables so at least it's plural?

[rudkx]

Lots of conflicts. It's easy enough to do a global rename at a later date; closing.