Previously, there was hacky code to deal with result locations and how
they work with regards to comptime values and runtime values. In
addition, there was a hacky "mem_slot" mechanism that managed the memory
for local variables, and acted differently depending on comptime vs
runtime situations. All that is deleted in this commit, and as a result,
result locations code has one less complication.

Importantly, this means that a comptime result location is now passed to
a function when it is evaluated at comptime.

This test causes many regressions, and some of the behavior tests are
disabled (commented out) in this commit. Future commits will re-enable
the tests before merging the branch.