[SCEV] Add predicated version of getSymbolicMaxBackedgeTakenCount. (#93498)

This patch adds a predicated version of
getSymbolicMaxBackedgeTakenCount.

The intended use for this is loop access analysis for loops with
uncountable exits. When analyzing dependences and computing runtime
checks, we need the smallest upper bound on the number of iterations. In
terms of memory safety, it shouldn't matter if any uncomputable exits
leave the loop, as long as we prove that there are no dependences given
the minimum of the countable exits. The same should apply also for
generating runtime checks.

PR: https://github.com/llvm/llvm-project/pull/93498