improve semi-concrete interpretation accuracy, take 2
Currently semi-concrete interpretation can end up with more inaccurate
result than usual abstract interpretation because `src.ssavaluetypes`
are all widened when cached so semi-concrete interpretation can't use
extended lattice information of `SSAValue`s. This commit tries to fix it
by making the codegen system recognize extended lattice information such
as `Const` and `PartialStruct` and not-widening those information from
`src::CodeInfo` when caching.
I found there are other chances when semi-concrete interpretation can
end up with inaccurate results, but that is unrelated to this and should
be fixed separately.
