These are very useful fixits for migration. Note: this applies the
fixits for selectors that are actually found, but not the one that wraps
an arbitrary string literal in Selector(...), because that one indicates
a possibly missing selector that the user should review.
rdar://problem/26678232
Now that we have ArchetypeBuilder::mapTypeOutOfContext(), we can
delete some tricky hand-crafted logic for getting the depth and
index of archetypes.
Notice that the depth of an archetype is now the same as generic
parameters, where depth 0 is the outermost generic context.
Previously it was backwards.
Mostly NFC, except that a few IDE crashers are now fixed because
of asserts firing in removed code, and also the change to depth
mangling (which I think makes sense, and it matches what's written
in docs/ABI.rst).
These interact badly with the swift migrator, they are triggered by label mismatches in pre-migrated code.
We also don't generally need them since we do inference for the most common cases.
