spirv: Handle the SpvDecorationStream decoration

From SPIR-V 1.0 spec, section 3.20, "Decoration":

   "Stream
    Apply to an object or a member of a structure type. Indicates the
    stream number to put an output on."

Note the "or", so that means that it is allowed for both a full struct
or a membef or a struct (although the wording is not really ideal, and
somewhat error-prone, imho).

We found this with some Geometry Streams tests for ARB_gl_spirv, where
the full gl_PerVertex is assigned Stream 0 (default value on OpenGL
for gl_PerVertex).

So this commit allows structs to have this Decoration, and sets the
stream at the nir variable if needed.

Signed-off-by: Neil Roberts <nroberts@igalia.com>
Signed-off-by: Alejandro Piñeiro <apinheiro@igalia.com>

v2: squash two Decoration Stream patches (Jason)

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/compiler/spirv/vtn_variables.c

@@ -1298,7 +1298,6 @@ apply_var_decoration(struct vtn_builder *b,
    case SpvDecorationMatrixStride:
    case SpvDecorationAliased:
    case SpvDecorationUniform:
-   case SpvDecorationStream:
    case SpvDecorationLinkageAttributes:
       break; /* Do nothing with these here */
 
@@ -1337,6 +1336,10 @@ apply_var_decoration(struct vtn_builder *b,
       var_data->offset = dec->literals[0];
       break;
 
+   case SpvDecorationStream:
+      var_data->stream = dec->literals[0];
+      break;
+
    case SpvDecorationCPacked:
    case SpvDecorationSaturatedConversion:
    case SpvDecorationFuncParamAttr: