glsl: Unify ir_constant::const_elements and ::components

glsl: Unify ir_constant::const_elements and ::components

There was no reason to treat array types and record types differently.
Unifying them saves a bunch of code and saves a few bytes in every
ir_constant.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Elie Tournier <elie.tournier@collabora.com>