Resolver: Validate resource binding decorations

Validate that:
* That resource variables have resource bindings
* Only resource variables have resource bindings
* That a [[binding]] decoration is paired with a [[group]]
* That binding points are not reused in the same entry point

Fixed: tint:235
Fixed: tint:645
Bug: tint:645
Change-Id: I2542934b4c6a2b4bbde48242932c04c796033a90
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/50500
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>

src/sem/binding_point.h

@@ -0,0 +1,70 @@
+// Copyright 2021 The Tint Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef SRC_SEM_BINDING_POINT_H_
+#define SRC_SEM_BINDING_POINT_H_
+
+#include <stdint.h>
+
+#include <functional>
+
+#include "src/utils/hash.h"
+
+namespace tint {
+namespace sem {
+
+/// BindingPoint holds a group and binding index.
+struct BindingPoint {
+  /// The `[[group]]` part of the binding point
+  uint32_t group = 0;
+  /// The `[[binding]]` part of the binding point
+  uint32_t binding = 0;
+
+  /// Equality operator
+  /// @param rhs the BindingPoint to compare against
+  /// @returns true if this BindingPoint is equal to `rhs`
+  inline bool operator==(const BindingPoint& rhs) const {
+    return group == rhs.group && binding == rhs.binding;
+  }
+
+  /// Inequality operator
+  /// @param rhs the BindingPoint to compare against
+  /// @returns true if this BindingPoint is not equal to `rhs`
+  inline bool operator!=(const BindingPoint& rhs) const {
+    return !(*this == rhs);
+  }
+};
+
+}  // namespace sem
+}  // namespace tint
+
+namespace std {
+
+/// Custom std::hash specialization for tint::sem::BindingPoint so
+/// BindingPoints can be used as keys for std::unordered_map and
+/// std::unordered_set.
+template <>
+class hash<tint::sem::BindingPoint> {
+ public:
+  /// @param binding_point the binding point to create a hash for
+  /// @return the hash value
+  inline std::size_t operator()(
+      const tint::sem::BindingPoint& binding_point) const {
+    return tint::utils::Hash(binding_point.group, binding_point.binding);
+  }
+};
+
+}  // namespace std
+
+#endif  // SRC_SEM_BINDING_POINT_H_