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/expressions/binary/left-shift/vector-vector/i32.wgsl.expected.glsl

@@ -8,8 +8,8 @@ void f() {
   ivec3 r = (a << b);
   return;
 }
+
 void main() {
   f();
 }
 
-

test/expressions/binary/left-shift/vector-vector/u32.wgsl.expected.glsl

@@ -8,8 +8,8 @@ void f() {
   uvec3 r = (a << b);
   return;
 }
+
 void main() {
   f();
 }
 
-