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/benchmark/animometer.wgsl b/test/tint/benchmark/animometer.wgsl
index b850d14..393c487 100644
--- a/test/tint/benchmark/animometer.wgsl
+++ b/test/tint/benchmark/animometer.wgsl
@@ -1,13 +1,13 @@
 struct Time {
-  value : f32;
+  value : f32,
 }
 
 struct Uniforms {
-  scale : f32;
-  offsetX : f32;
-  offsetY : f32;
-  scalar : f32;
-  scalarOffset : f32;
+  scale : f32,
+  offsetX : f32,
+  offsetY : f32,
+  scalar : f32,
+  scalarOffset : f32,
 }
 
 @binding(0) @group(0) var<uniform> time : Time;
@@ -16,9 +16,9 @@
 
 struct VertexOutput {
   @builtin(position)
-  Position : vec4<f32>;
+  Position : vec4<f32>,
   @location(0)
-  v_color : vec4<f32>;
+  v_color : vec4<f32>,
 }
 
 @stage(vertex)