glsl/st: move has_half_float_packing flag to consts struct

Moving this out of the state tracker will allow us to move its user
directly to the glsl linker in the folowing patch.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26628>

src/mesa/main/consts_exts.h

@@ -752,6 +752,8 @@ struct gl_constants
     */
    GLboolean GLSLSkipStrictMaxUniformLimitCheck;
 
+   GLboolean GLSLHasHalfFloatPacking;
+
    /**
     * Whether gl_FragCoord, gl_PointCoord and gl_FrontFacing
     * are system values.

src/mesa/state_tracker/st_context.c

@@ -595,7 +595,7 @@ st_create_context_priv(struct gl_context *ctx, struct pipe_context *pipe,
       !screen->get_param(screen, PIPE_CAP_GL_CLAMP);
    st->has_time_elapsed =
       screen->get_param(screen, PIPE_CAP_QUERY_TIME_ELAPSED);
-   st->has_half_float_packing =
+   ctx->Const.GLSLHasHalfFloatPacking =
       screen->get_param(screen, PIPE_CAP_SHADER_PACK_HALF_FLOAT);
    st->has_multi_draw_indirect =
       screen->get_param(screen, PIPE_CAP_MULTI_DRAW_INDIRECT);

src/mesa/state_tracker/st_context.h

@@ -159,7 +159,6 @@ struct st_context
    bool force_specialized_compute_transfer;
    bool force_persample_in_shader;
    bool has_shareable_shaders;
-   bool has_half_float_packing;
    bool has_multi_draw_indirect;
    bool has_indirect_partial_stride;
    bool has_occlusion_query;

src/mesa/state_tracker/st_glsl_to_nir.cpp

@@ -511,7 +511,7 @@ st_link_glsl_to_nir(struct gl_context *ctx,
 
          lower_packing_builtins(ir, ctx->Extensions.ARB_shading_language_packing,
                                 ctx->Extensions.ARB_gpu_shader5,
-                                ctx->st->has_half_float_packing);
+                                ctx->Const.GLSLHasHalfFloatPacking);
          do_mat_op_to_vec(ir);
 
          lower_instructions(ir, ctx->Extensions.ARB_gpu_shader5);