[NVPTX] fixup support for over-aligned parameters (#92457)

This extends the NVPTX support for over-aligned parameters and return
values in a few related ways:

- Support for `alignstack` attribute, as an alternative to legacy nvvm
`!"align"` metadata entries. While we still maintain the legacy support,
long term it might be nice to auto-upgrade to `alignstack`.
- Check the alignment info when emitting the parameter list to prevent a
mismatch between alignment of caller and callee, which would previously
cause a fatal error for `ptxas`.
- Check the alignment info when emitting loads for parameters,
potentially enabling better vectorization.