[TableGen] Support creating multi-result ops in result patterns

[TableGen] Support creating multi-result ops in result patterns

This CL introduces a new syntax for creating multi-result ops and access their
results in result patterns. Specifically, if a multi-result op is unbound or
bound to a name without a trailing `__N` suffix, it will act as a value pack
and expand to all its values. If a multi-result op is bound to a symbol with
`__N` suffix, only the N-th result will be extracted and used.

PiperOrigin-RevId: 256465208