glsl: Use alignment of container record for its first field

glsl: Use alignment of container record for its first field

The first field of a record in a UBO has the aligment of the record
itself.

Fixes piglit vs-struct-pad, fs-struct-pad, and (with the patch posted to
the piglit list that extends the test) layout-std140.

NOTE: The bit of strangeness with the version of visit_field without the
record_type poitner is because that method is pure virtual in the base
class.  The original implementation of the class did this to ensure
derived classes remembered to implement that flavor.  Now they can
implement either flavor but not both.  I don't know a C++ way to enforce
that.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Paul Berry <stereotype441@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=68195
Cc: "9.2 9.1" mesa-stable@lists.freedesktop.org