Expose React Native version as a symbol rather than macro

Summary:
Add RCTGetReactNativeVersion() to expose version in native code. Right now, version is exposed internally to RN using a MACRO constant. This exposes a symbol (function) that can be called to retrieve the React Native version in iOS.

Also exposed RCTVersion.h as a public header in the React project so it is available to developers.

The motivation behind this is for https://github.com/wix/detox —we need to know what RN version the user has, if any, so we can properly handle support and abstract differences.

Ran bump-oss-version.js to ensure the template is applied properly. Also compiled the project to make sure nothing is broken.

 [IOS] [ENHANCEMENT] [RCTVersion.h] - Expose version as a compile-time symbol for native queries

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 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
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-->
Closes https://github.com/facebook/react-native/pull/18136

Differential Revision: D7141076

Pulled By: hramos

fbshipit-source-id: 18a92b8c60d7b43fa0ed22597ea46a35cff73c56

scripts/bump-oss-version.js

@@ -67,8 +67,8 @@ fs.writeFileSync(
 );
 
 fs.writeFileSync(
-  'React/Base/RCTVersion.h',
-  cat('scripts/versiontemplates/RCTVersion.h.template')
+  'React/Base/RCTVersion.m',
+  cat('scripts/versiontemplates/RCTVersion.m.template')
     .replace('${major}', `@(${major})`)
     .replace('${minor}', `@(${minor})`)
     .replace('${patch}', `@(${patch})`)

scripts/versiontemplates/RCTVersion.h.template

@@ -1,15 +0,0 @@
-/**
- * @generated by scripts/bump-oss-version.js
- *
- * Copyright (c) 2015-present, Facebook, Inc.
- *
- * This source code is licensed under the MIT license found in the
- * LICENSE file in the root directory of this source tree.
- */
-
-#define RCT_REACT_NATIVE_VERSION @{ \
-  @"major": ${major}, \
-  @"minor": ${minor}, \
-  @"patch": ${patch}, \
-  @"prerelease": ${prerelease}, \
-}

scripts/versiontemplates/RCTVersion.m.template

@@ -0,0 +1,33 @@
+/**
+ * @generated by scripts/bump-oss-version.js
+ *
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#import "RCTVersion.h"
+
+NSString* const RCTVersionMajor = @"major";
+NSString* const RCTVersionMinor = @"minor";
+NSString* const RCTVersionPatch = @"patch";
+NSString* const RCTVersionPrerelease = @"prerelease";
+
+static NSDictionary* __rnVersion;
+
+__attribute__((constructor))
+static void __makeVersion()
+{
+  __rnVersion = @{
+                  RCTVersionMajor: ${major},
+                  RCTVersionMinor: ${minor},
+                  RCTVersionPatch: ${patch},
+                  RCTVersionPrerelease: ${prerelease},
+                  };
+}
+
+NSDictionary* RCTGetReactNativeVersion(void)
+{
+  return __rnVersion;
+}