test: Split binary_expressions into separate tests

Tests should be as fine-grained as possible.
Not all the permutations were covered.
Not all the backends were actually generating anything useful, as the
functions were not called by an entry point.

Change-Id: I76658533d3112d202f7482a19531079550e66f83
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/58392
Auto-Submit: Ben Clayton <bclayton@google.com>
Commit-Queue: David Neto <dneto@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: David Neto <dneto@google.com>
diff --git a/test/expressions/binary/bit-xor/scalar-scalar/i32.wgsl.expected.hlsl b/test/expressions/binary/bit-xor/scalar-scalar/i32.wgsl.expected.hlsl
new file mode 100644
index 0000000..f3a33ad
--- /dev/null
+++ b/test/expressions/binary/bit-xor/scalar-scalar/i32.wgsl.expected.hlsl
@@ -0,0 +1,5 @@
+[numthreads(1, 1, 1)]
+void f() {
+  const int r = (1 ^ 2);
+  return;
+}