This is partly to tidy things up, but also a good test for 'import as'.
Requires some internal changes since there are parts of reflection,
unelaboration and a compiler hack that rely on where things are in the
Prelude.
On the LHS, we want to match against the reflected thing, so FC and
implicits need to turn into match anything patterns, or we won't match
anything at all. This means we can put quoted terms on the LHS, with
pattern variables under ~().