nir: Add new linking helper to set linked driver locations.

nir: Add new linking helper to set linked driver locations.

This commit introduces a new function nir_assign_linked_io_var_locations
which is intended to help with assigning driver locations to shaders
during linking, primarily aimed at the VS->TCS->TES->GS stages.

It ensures that the linked shaders have the same driver locations,
and it also packs these as close to each other as possible.

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4388>