[SelectionDAG][Statepoint] Fix truncation of `gc.statepoint` ID argument (#85908)

The ID argument of `gc.statepoint` gets incorrectly truncated to 32 bits
during code generation.
This is fixed by using `uint64_t` instead of `unsigned` for the `ID`
member in `SelectionDAGBuilder::StatepointLoweringInfo`, and a
`patchpoint` test case is extended to check for 64 bit ID generation in
stackmaps.