tint: Add support for atomic ops to spirv reader

The following operations are supported:

OpAtomicLoad
OpAtomicStore
OpAtomicExchange
OpAtomicCompareExchange
OpAtomicCompareExchangeWeak
OpAtomicIIncrement
OpAtomicIDecrement
OpAtomicIAdd
OpAtomicISub
OpAtomicSMin
OpAtomicUMin
OpAtomicSMax
OpAtomicUMax
OpAtomicAnd
OpAtomicOr
OpAtomicXor

These are not, but may be supported in the future:

OpAtomicFlagTestAndSet
OpAtomicFlagClear
OpAtomicFMinEXT
OpAtomicFMaxEXT
OpAtomicFAddEXT

Bug: tint:1441
Change-Id: Ifd53643b38d43664905a0dddfca609add4914670
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/94121
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>

test/tint/builtins/atomicStore/struct/array_of_struct.spvasm.expected.wgsl

@@ -0,0 +1,52 @@
+struct S_atomic {
+  x : i32,
+  a : atomic<u32>,
+  y : u32,
+}
+
+struct S {
+  x : i32,
+  a : u32,
+  y : u32,
+}
+
+type Arr = array<S, 10u>;
+
+var<private> local_invocation_index_1 : u32;
+
+var<workgroup> wg : array<S_atomic, 10u>;
+
+fn compute_main_inner(local_invocation_index : u32) {
+  var idx : u32 = 0u;
+  idx = local_invocation_index;
+  loop {
+    let x_23 : u32 = idx;
+    if (!((x_23 < 10u))) {
+      break;
+    }
+    let x_28 : u32 = idx;
+    wg[x_28].x = 0i;
+    atomicStore(&(wg[x_28].a), 0u);
+    wg[x_28].y = 0u;
+
+    continuing {
+      let x_41 : u32 = idx;
+      idx = (x_41 + 1u);
+    }
+  }
+  workgroupBarrier();
+  atomicStore(&(wg[4i].a), 1u);
+  return;
+}
+
+fn compute_main_1() {
+  let x_53 : u32 = local_invocation_index_1;
+  compute_main_inner(x_53);
+  return;
+}
+
+@compute @workgroup_size(1i, 1i, 1i)
+fn compute_main(@builtin(local_invocation_index) local_invocation_index_1_param : u32) {
+  local_invocation_index_1 = local_invocation_index_1_param;
+  compute_main_1();
+}