wgsl: Separate struct members with commas

Use of semicolons is still supported, but deprecated.

Also updates the parsing methods for structures to better match the
WGSL grammar.

Bug: tint:1475
Change-Id: I7675ba42c13f91080b0ac173c352e0092021f80b
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/84380
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: James Price <jrprice@google.com>
diff --git a/test/tint/vk-gl-cts/graphicsfuzz/cov-value-tracking-apint-inst-combine-simplify-one-mod-loop-iterator/0-opt.wgsl b/test/tint/vk-gl-cts/graphicsfuzz/cov-value-tracking-apint-inst-combine-simplify-one-mod-loop-iterator/0-opt.wgsl
index 037beb4..f609495 100644
--- a/test/tint/vk-gl-cts/graphicsfuzz/cov-value-tracking-apint-inst-combine-simplify-one-mod-loop-iterator/0-opt.wgsl
+++ b/test/tint/vk-gl-cts/graphicsfuzz/cov-value-tracking-apint-inst-combine-simplify-one-mod-loop-iterator/0-opt.wgsl
@@ -1,12 +1,12 @@
 struct strided_arr {
   @size(16)
-  el : i32;
+  el : i32,
 }
 
 type Arr = array<strided_arr, 4u>;
 
 struct buf0 {
-  x_GLF_uniform_int_values : Arr;
+  x_GLF_uniform_int_values : Arr,
 }
 
 @group(0) @binding(0) var<uniform> x_6 : buf0;
@@ -58,7 +58,7 @@
 
 struct main_out {
   @location(0)
-  x_GLF_color_1 : vec4<f32>;
+  x_GLF_color_1 : vec4<f32>,
 }
 
 @stage(fragment)