compiler: Move double_inputs to gl_program::DualSlotInputs

Previously, we had two field in shader_info: double_inputs_read and
double_inputs.  Presumably, the one was for all double inputs that are
read and the other is all that exist.  However, because nir_gather_info
regenerates these two values, there is a possibility, if a variable gets
deleted, that the value of double_inputs could change over time.  This
is a problem because double_inputs is used to remap the input locations
to a two-slot-per-dvec3/4 scheme for i965.  If that mapping were to
change between glsl_to_nir and back-end state setup, we would fall over
when trying to map the NIR outputs back onto the GL location space.

This commit changes the way slot re-mapping works.  Instead of the
double_inputs field in shader_info, it adds a DualSlotInputs bitfield to
gl_program.  By having it in gl_program, we more easily guarantee that
NIR passes won't touch it after it's been set.  It also makes more sense
to put it in a GL data structure since it's really a mapping from GL
slots to back-end and/or NIR slots and not really a NIR shader thing.

Tested-by: Alejandro Piñeiro <apinheiro@igalia.com> (ARB_gl_spirv tests)
Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/compiler/nir/nir.h

@@ -3039,8 +3039,10 @@ bool nir_opt_conditional_discard(nir_shader *shader);
 
 void nir_sweep(nir_shader *shader);
 
-void nir_remap_attributes(nir_shader *shader,
-                          const nir_shader_compiler_options *options);
+uint64_t nir_get_dual_slot_attributes(nir_shader *shader);
+void nir_remap_dual_slot_attributes(nir_shader *shader,
+                                    uint64_t dual_slot);
+uint64_t nir_get_single_slot_attribs_mask(uint64_t attribs, uint64_t dual_slot);
 
 nir_intrinsic_op nir_intrinsic_from_system_value(gl_system_value val);
 gl_system_value nir_system_value_from_intrinsic(nir_intrinsic_op intrin);