wgsl: Add support for increment/decrement statements

Implemented in both the reader and writer with E2E tests. Other
backends will ICE for now.

Bug: tint:1488
Change-Id: Ied2afa55a338347f427dee98a4076643ac432d9c
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/86003
Reviewed-by: Ben Clayton <bclayton@google.com>
diff --git a/test/tint/statements/increment/for_loop_initializer.wgsl.expected.hlsl b/test/tint/statements/increment/for_loop_initializer.wgsl.expected.hlsl
new file mode 100644
index 0000000..1fa9624
--- /dev/null
+++ b/test/tint/statements/increment/for_loop_initializer.wgsl.expected.hlsl
@@ -0,0 +1,11 @@
+SKIP: FAILED
+
+
+@group(0) @binding(0) var<storage, read_write> i : u32;
+
+fn main() {
+  for(i++; (i < 10u); ) {
+  }
+}
+
+Failed to generate: error: cannot modify value of type 'u32'