Fair Return Types

[timcassell]

Follow-up to #2334. Fixes #2305.

All return types are treated equally. No more special consume logic for ByRef, or struct return types. Return values are popped off the stack instead of passed to Consumer or a NoInlining method. This is able to be done while avoiding dead code elimination by taking advantage of the changes made in #2334.

Overhead return type is always void now for a fair baseline.

Also fixed pointer returns in InProcessEmitToolchain.

[timcassell]

@AndreyAkinshin I moved this to v0.14.0 milestone because I think both #2334 and this should go out in the same version so that we are only affecting measurement accuracy in a single version, rather than multiple versions. If we can't get them both in v0.14.0, let's push them both out.