Some requirement machine work
Rename requirement to Value
Rename more things to Value
Fix integer checking for requirement
some docs and parser changes
Minor fixes
This removes the "optimization" where a function type, metatype or
tuple type was split up into structural components, because it seems
that in general we need this structural type metadata again.
Similarly, this no longer tries to split up dependent concrete
conformances and instead passes the witness table in the context.
This makes the context larger potentially, but it avoids calls to
metadata access functions and swift_getWitnessTable() every time the
closure is invoked.
A lot of the fixes here are adjustments to compensate in the
fulfillment and metadata-path subsystems for the recent pack
substitutions representation change. I think these adjustments
really make the case for why the change was the right one to make:
the code was clearly not considering the possibility of packs
in these positions, and the need to handle packs makes everything
work out much more cleanly.
There's still some work that needs to happen around type packs;
in particular, we're not caching them or fulfilling them as a
whole, and we do have the setup to do that properly now.
Added pack flavors of requirement kinds for metadata and witness tables.
Fixes the function signatures for variadic generic functions which
previously used %swift.type* for variadic generic parameters--those are
lists of metadata and should actually be %swift.type**.
