glsl: fix uniform linking logic in the presence of structs

glsl: fix uniform linking logic in the presence of structs

Add a enter/leave record callback so that the offset may be aligned to
the proper value. Otherwise only leaf fields are called, and the first
field needs to be aligned to the outer struct's base alignment while the
last field needs to be aligned to the inner struct's base alignment.

This removes most usage of the last field/record type values passed into
visit_field.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Dave Airlie <airlied@redhat.com>