[CIR][NFC] Sort emit functions in CIRGenFunction.h (#1524)

This change moves all declarations of emit* functions in
CIRGenFunction.h into a common location and sorts them alphabetically.
The goal of this change is to make it easier to keep upstream and
incubator code in a consistent location, making functions easier to find
for upstreaming and minimizing conflicts in the incubator when rebasing.

I did most of this sort manually, and I've probably been inconsistent in
how I treat sorting of uppercase versus lowercase. I made no attempt to
provide a rule for ordering different declarations of functions with the
same name. We can improve on that over time if anyone feels the need.

I tried very hard not to drop comments (one of the reasons I had to do
this manually), but I may have lost a few.

This change loses the grouping of some declarations that were co-located
by common purpose, but most of the declarations lacked a coherent
ordering, so I think this is a step forward overall.

Author: andykaylor