[glsl] Use vector component notation in more places

This makes the generated GLSL easier to read and slightly shorter.

Change-Id: If3da1843ca1aa864048f6dfb7d5f59474f9d3258
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/217255
Commit-Queue: James Price <jrprice@google.com>
Reviewed-by: dan sinclair <dsinclair@chromium.org>
diff --git a/test/tint/builtins/gen/var/textureDimensions/2e443d.wgsl.expected.glsl b/test/tint/builtins/gen/var/textureDimensions/2e443d.wgsl.expected.glsl
index 31cf17e..57b8ed3 100644
--- a/test/tint/builtins/gen/var/textureDimensions/2e443d.wgsl.expected.glsl
+++ b/test/tint/builtins/gen/var/textureDimensions/2e443d.wgsl.expected.glsl
@@ -84,8 +84,8 @@
 void main() {
   VertexOutput v_2 = vertex_main_inner();
   gl_Position = v_2.pos;
-  gl_Position[1u] = -(gl_Position.y);
-  gl_Position[2u] = ((2.0f * gl_Position.z) - gl_Position.w);
+  gl_Position.y = -(gl_Position.y);
+  gl_Position.z = ((2.0f * gl_Position.z) - gl_Position.w);
   vertex_main_loc0_Output = v_2.prevent_dce;
   gl_PointSize = 1.0f;
 }