* Remove some allocations in `CodeMemory`
This commit removes the `FinishedFunctions` type as well as allocations
associated with trampolines when allocating inside of a `CodeMemory`.
The main goal of this commit is to improve the time spent in
`CodeMemory` where currently today a good portion of time is spent
simply parsing symbol names and trying to extract function indices from
them. Instead this commit implements a new strategy (different from #3236)
where compilation records offset/length information for all
functions/trampolines so this doesn't need to be re-learned from the
object file later.
A consequence of this commit is that this offset information will be
decoded/encoded through `bincode` unconditionally, but we can also
optimize that later if necessary as well.
Internally this involved quite a bit of refactoring since the previous
map for `FinishedFunctions` was relatively heavily relied upon.
* comments
a237e73b5a