writer/hlsl: Simplify emission logic, clean up output

And fix issues where global variables would not be emitted unless they were transitively referenced by an entry point.

This change requires crbug.com/tint/697 to be fixed before landing.

Change-Id: I712bd9d369e08c9a3cdfb0f114c3609584f91f28
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/54241
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: James Price <jrprice@google.com>

test/ptr_ref/load/global/i32.spvasm.expected.hlsl

@@ -6,4 +6,3 @@ void main() {
   const int x_11 = (x_9 + 1);
   return;
 }
-

test/ptr_ref/load/global/i32.wgsl.expected.hlsl

@@ -6,4 +6,3 @@ void main() {
   const int use = (i + 1);
   return;
 }
-

test/ptr_ref/load/global/struct_field.spvasm.expected.hlsl

@@ -11,4 +11,3 @@ void main() {
   i = x_15;
   return;
 }
-

test/ptr_ref/load/global/struct_field.wgsl.expected.hlsl

@@ -9,4 +9,3 @@ void main() {
   const int i = V.i;
   return;
 }
-

test/ptr_ref/load/local/i32.spvasm.expected.hlsl

@@ -6,4 +6,3 @@ void main() {
   const int x_12 = (x_10 + 1);
   return;
 }
-

test/ptr_ref/load/local/i32.wgsl.expected.hlsl

@@ -4,4 +4,3 @@ void main() {
   const int use = (i + 1);
   return;
 }
-

test/ptr_ref/load/local/ptr_function.wgsl.expected.hlsl

@@ -4,4 +4,3 @@ void main() {
   const int use = (i + 1);
   return;
 }
-

test/ptr_ref/load/local/ptr_private.wgsl.expected.hlsl

@@ -5,4 +5,3 @@ void main() {
   const int use = (i + 1);
   return;
 }
-

test/ptr_ref/load/local/ptr_storage.wgsl.expected.hlsl

@@ -1,4 +1,3 @@
-
 RWByteAddressBuffer v : register(u0, space0);
 
 [numthreads(1, 1, 1)]
@@ -6,4 +5,3 @@ void main() {
   const int use = (asint(v.Load(0u)) + 1);
   return;
 }
-

test/ptr_ref/load/local/ptr_uniform.wgsl.expected.hlsl

@@ -9,4 +9,3 @@ void main() {
   const int use = (v.a + 1);
   return;
 }
-

test/ptr_ref/load/local/ptr_workgroup.wgsl.expected.hlsl

@@ -6,4 +6,3 @@ void main() {
   const int use = (i + 1);
   return;
 }
-

test/ptr_ref/load/local/struct_field.spvasm.expected.hlsl

@@ -10,4 +10,3 @@ void main() {
   i = x_14;
   return;
 }
-

test/ptr_ref/load/local/struct_field.wgsl.expected.hlsl

@@ -8,4 +8,3 @@ void main() {
   int i = V.i;
   return;
 }
-

test/ptr_ref/load/param/ptr.spvasm.expected.hlsl

@@ -11,4 +11,3 @@ void main() {
   const int x_18 = func(x_19, i);
   return;
 }
-

test/ptr_ref/load/param/ptr.wgsl.expected.hlsl

@@ -8,4 +8,3 @@ void main() {
   const int r = func(i, i);
   return;
 }
-