Surprisingly, there are some situations where an extension can end up
with _fewer_ constraints than the extended type. That was baked-in as an
assertion in this new-ish method.
I haven't figured out why that can happen in the reproducer only when
using `-interpret` mode. It didn't trigger the assertion for me when
compiling normally.
The fix is simple: check all the requirements, rather than using a
short-cut.
resolves rdar://125659789 / https://github.com/apple/swift/issues/72719
