spirv-reader: Set workgroup size, but not specializable

The WorkgroupSize builtin decoration applies to a composite constant.
Because WGSL does not yet support specializable constants for this,
use the *default* values for that SPIR-V spec constant.

Update end-to-end test expectations.

Fixed: tint:503
Change-Id: I012b316d13544ab9282e3276b58906327adab133
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/41960
Auto-Submit: David Neto <dneto@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: David Neto <dneto@google.com>
Reviewed-by: Alan Baker <alanbaker@google.com>

test/ptr_ref/load/global/i32.spvasm.expected.wgsl

@@ -6,7 +6,7 @@ fn main_1() {
   return;
 }
 
-[[stage(compute)]]
+[[stage(compute), workgroup_size(1, 1, 1)]]
 fn main() {
   main_1();
 }

test/ptr_ref/load/global/struct_field.spvasm.expected.wgsl

@@ -11,7 +11,7 @@ fn main_1() {
   return;
 }
 
-[[stage(compute)]]
+[[stage(compute), workgroup_size(1, 1, 1)]]
 fn main() {
   main_1();
 }

test/ptr_ref/load/local/i32.spvasm.expected.wgsl

@@ -6,7 +6,7 @@ fn main_1() {
   return;
 }
 
-[[stage(compute)]]
+[[stage(compute), workgroup_size(1, 1, 1)]]
 fn main() {
   main_1();
 }

test/ptr_ref/load/local/struct_field.spvasm.expected.wgsl

@@ -10,7 +10,7 @@ fn main_1() {
   return;
 }
 
-[[stage(compute)]]
+[[stage(compute), workgroup_size(1, 1, 1)]]
 fn main() {
   main_1();
 }

test/ptr_ref/load/param/ptr.spvasm.expected.wgsl

@@ -11,7 +11,7 @@ fn main_1() {
   return;
 }
 
-[[stage(compute)]]
+[[stage(compute), workgroup_size(1, 1, 1)]]
 fn main() {
   main_1();
 }