JIT: optimize redundant type tests created by PGO

[AndyAyersMS]

It seems likely that many of the type tests introduced by the jit will be redundant, as multiple virtual or interface calls can be made on the same object.

A first step towards optimizing these is the jump threading introduced in #46257, but this should be generalized to handle the case where there is computation in between the calls. In general this computation must be duplicated so in addition to the logistics of properly duplicating the code, some heuristics will be needed to decide when the duplication is worthwhile.

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[AndyAyersMS]

It might also make sense to try and catch this earlier during fgOptimizeUncondBranchToSimpleCond so that in cases with back to back type tests on the same object the paths are disambiguated before we get to the optimizer.

[AndyAyersMS]

#51890 gets many cases of this even earlier (during guarded devirt transform). But likely we'll want enhancements elsewhere as opportunities will arise downstream.