This will allow us to run two different completion kinds and deliver results from both of them.
Also: Compute a unified type context for global lookup. Previously, we always used the expected type context of the last lookup. But really, we should be considering all possible types from all constraint system solutions when computing code completion results from the cache.
Only return macros that are valid in their current position, ie. an
attached macro is not valid on a nominal.
Also return freestanding expression macros in code block item position
and handle the new freestanding code item macros.
Resolves rdar://105563583.
We don't need special completion logic for things like `#file` and
`#line` now that they are declared in the standard library. Drop it
and update tests.
