JIT: add a bit more importer folding (#16111)
JIT: add a bit more importer folding (#16111)

Eagerly fold expression trees for non-branch conditional operations.

Leads to elimination of boxes in some idiomatic uses. See notes and
examples in #14472.
cshung/coreclr,wtgodbe/coreclr,mmitche/coreclr,ruben-ayrapetyan/coreclr,ruben-ayrapetyan/coreclr,wtgodbe/coreclr,krk/coreclr,wtgodbe/coreclr,yizhang82/coreclr,krk/coreclr,ruben-ayrapetyan/coreclr,krk/coreclr,cshung/coreclr,yizhang82/coreclr,cshung/coreclr,yizhang82/coreclr,yizhang82/coreclr,poizan42/coreclr,yizhang82/coreclr,yizhang82/coreclr,ruben-ayrapetyan/coreclr,poizan42/coreclr,krk/coreclr,wtgodbe/coreclr,poizan42/coreclr,ruben-ayrapetyan/coreclr,mmitche/coreclr,krk/coreclr,wtgodbe/coreclr,poizan42/coreclr,wtgodbe/coreclr,krk/coreclr,cshung/coreclr,mmitche/coreclr,mmitche/coreclr,mmitche/coreclr,mmitche/coreclr,cshung/coreclr,ruben-ayrapetyan/coreclr,poizan42/coreclr,poizan42/coreclr,cshung/coreclr