Abstract underlying Color implementation

Summary:
On other platforms (e.g., react-native-windows), it's possible that platform colors may not be efficiently represented as int32_t values. In the case of react-native-windows, Color can either be an ARGB value or a list of fallback strings for platform colors.

This change should decouple how platforms represent color values, allowing them to manage how they are used at the point they are used.

## Changelog:
[General] [Added] - Support customization of underlying Color representation in out-of-tree platforms

Differential Revision: D47873465

fbshipit-source-id: 8715b3061f4280e118fb6e39971d604137003d07

packages/react-native/ReactCommon/react/renderer/graphics/Color.h

@@ -12,16 +12,17 @@
 #include <limits>
 
 #include <react/renderer/graphics/ColorComponents.h>
+#include <react/renderer/graphics/HostPlatformColor.h>
 
 namespace facebook::react {
 
-using Color = int32_t;
-
 /*
  * On Android, a color can be represented as 32 bits integer, so there is no
  * need to instantiate complex color objects and then pass them as shared
  * pointers. Hense instead of using shared_ptr, we use a simple wrapper class
- * which provides a pointer-like interface.
+ * which provides a pointer-like interface. On other platforms, colors may be
+ * represented by more complex objects that cannot be represented as 32-bits
+ * integers, so we hide the implementation detail in HostPlatformColor.h.
  */
 class SharedColor {
  public:

packages/react-native/ReactCommon/react/renderer/graphics/platform/android/react/renderer/graphics/HostPlatformColor.h

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+namespace facebook::react {
+
+using Color = int32_t;
+
+} // namespace facebook::react

packages/react-native/ReactCommon/react/renderer/graphics/platform/cxx/react/renderer/graphics/HostPlatformColor.h

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+namespace facebook::react {
+
+using Color = int32_t;
+
+} // namespace facebook::react

packages/react-native/ReactCommon/react/renderer/graphics/platform/ios/react/renderer/graphics/HostPlatformColor.h

@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+namespace facebook::react {
+
+using Color = int32_t;
+
+} // namespace facebook::react