[SelectionDAG] Add space-optimized forms of OPC_CheckPredicate (#77763)

We record the usage of each `Predicate` and sort them by usage.

For the top 8 `Predicate`s, we will emit a `PC_CheckPredicateN` to
save one byte.

Overall this reduces the llc binary size with all in-tree targets by
about 61K.

This is a recommit of 1a579273, which was reverted in bc98c310.

The CI failures occurred when doing expensive checks (with option
`LLVM_ENABLE_EXPENSIVE_CHECKS` being ON).

The key point here is that we need stable sorting result in the
test, but doing expensive checks uncovered the non-determinism of
`llvm::sort`. So `llvm::sort` is changed to `llvm::stable_sort`
in this revised patch.

And we use `llvm::MapVector` to keep insertion order.