This basically undoes 3da6fe9c0d, which in hindsight was wrong.
There were no other usages of TypeArrayView anywhere else except for
GenericSignature::getGenericParams(), and it was almost never what
you want, so callers had to convert back and forth to an ArrayRef.
Remove it.
The root potential archetypes in an archetype builder are associated
with generic parameters. Start decoupling potential archetypes from a
specific GenericTypeParamType and instead work with the abstracted
depth/index. The goal here is to allow the same archetype builder to
be used within different generic environments (which includes both
different generic parameters and different archetypes).
As part of this, boost the archetype builder's GenericTypeParamKey
from a local type to a more generic GenericParamKey that can be used
in other interfaces that want to work with abstracted generic
parameters.
