[TableGen][GISel] Fix incorrect binding of predicate operands upon...

[TableGen][GISel] Fix incorrect binding of predicate operands upon `PredicateUsesOperands = 1` (#68125)

When `PredicateUsesOperands` is set to true, GlobalISelEmitter preserves
the original index of predicate operands and uses that information on
each predicate usage. However, previously it only looked up the original
index for "actual" operands (i.e. operands of a predicate usage) that
are leaf nodes, which is an incorrect assumption.
This patch fix it by generalizing the acceptable kinds of actual
operands for predicate as well as checking the existance of bound
predicate operands.