GLSL: clean up GLSL output whitespace generation.

More line() and less std::endl.
More automated indents and less manual spacing.
Put a single newline after every struct and function declaration.

Note that this does touch every test result, but only affects whitespace.

Change-Id: I7506b9029b79b91fb335911dba44369b36f09bbe
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/78300
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Stephen White <senorblanco@chromium.org>

test/buffer/uniform/static_index/read.wgsl.expected.glsl

@@ -4,6 +4,7 @@ precision mediump float;
 struct Inner {
   int x;
 };
+
 struct S {
   ivec3 a;
   int b;
@@ -50,8 +51,8 @@ void tint_symbol() {
   Inner l[4] = s.l;
   return;
 }
+
 void main() {
   tint_symbol();
 }
 
-