Start using getConstants

Summary:
TurboModules depend on a getConstants method. Existing ObjectiveC modules do not have this method. Therefore, I moved the contents of `constantsToExport` to `getConstants` and then had `constantsToExports` call `getConstants`.

facebook
Since all NativeModules will eventually need to be migrated to the TurboModule system, I didn't restrict this to just the NativeModules in Marketplace.

```
const fs = require('fs');

if (process.argv.length < 3) {
    throw new Error('Expected a file containing a list of native modules as the third param');
}

function read(filename) {
    return fs.readFileSync(filename, 'utf8');
}

const nativeModuleFilenames = read(process.argv[2]).split('\n').filter(Boolean);

nativeModuleFilenames.forEach((fileName) => {
    if (fileName.endsWith('.h')) {
        return;
    }

    const absPath = `${process.env.HOME}/${fileName}`;
    const fileSource = read(absPath);

    if (/(\n|^)-\s*\((.+)\)getConstants/.test(fileSource)) {
        return;
    }

    const constantsToExportRegex = /(\n|^)-\s*\((.+)\)constantsToExport/;
    const result = constantsToExportRegex.exec(fileSource);

    if (result == null) {
        throw new Error(`Didn't find a constantsToExport function inside NativeModule ${fileName}`);
    }

    const returnType = result[2];

    const newFileSource = fileSource.replace(
        constantsToExportRegex,
        '$1- ($2)constantsToExport\n' +
        '{\n' +
        `  return ${returnType.includes('ModuleConstants') ? '($2)' : ''}[self getConstants];\n` +
        '}\n' +
        '\n' +
        '- ($2)getConstants'
    );

    fs.writeFileSync(absPath, newFileSource);
});
```

```
> xbgs -l ')constantsToExport'
```

Reviewed By: fkgozali

Differential Revision: D13951197

fbshipit-source-id: 394a319d42aff466c56a3d748e17c335307a8f47

Libraries/Blob/RCTBlobManager.mm

@@ -48,6 +48,11 @@ RCT_EXPORT_MODULE(BlobModule)
 }
 
 - (NSDictionary<NSString *, id> *)constantsToExport
+{
+  return [self getConstants];
+}
+
+- (NSDictionary<NSString *, id> *)getConstants
 {
   return @{
     @"BLOB_URI_SCHEME": kBlobURIScheme,

Libraries/Settings/RCTSettingsManager.m

@@ -52,6 +52,11 @@ RCT_EXPORT_MODULE()
 }
 
 - (NSDictionary<NSString *, id> *)constantsToExport
+{
+  return [self getConstants];
+}
+
+- (NSDictionary<NSString *, id> *)getConstants
 {
   return @{@"settings": RCTJSONClean([_defaults dictionaryRepresentation])};
 }

RNTester/RNTesterUnitTests/RCTModuleInitTests.m

@@ -90,6 +90,11 @@ RCT_EXPORT_MODULE()
 RCT_EXPORT_MODULE()
 
 - (NSDictionary<NSString *, id> *)constantsToExport
+{
+  return [self getConstants];
+}
+
+- (NSDictionary<NSString *, id> *)getConstants
 {
   _exportedConstants = YES;
   _exportedConstantsOnMainQueue = RCTIsMainQueue();

React/Base/RCTPlatform.m

@@ -37,6 +37,11 @@ RCT_EXPORT_MODULE(PlatformConstants)
 }
 
 - (NSDictionary<NSString *, id> *)constantsToExport
+{
+  return [self getConstants];
+}
+
+- (NSDictionary<NSString *, id> *)getConstants
 {
   UIDevice *device = [UIDevice currentDevice];
   return @{

React/CxxModule/RCTCxxModule.mm

@@ -64,7 +64,12 @@ using namespace facebook::react;
   return moduleMethods;
 }
 
-- (NSDictionary<NSString *, id> *)constantsToExport;
+- (NSDictionary<NSString *, id> *)constantsToExport
+{
+  return [self getConstants];
+}
+
+- (NSDictionary<NSString *, id> *)getConstants;
 {
   [self lazyInit];
   if (!_module) {

React/Modules/RCTAppState.m

@@ -48,6 +48,11 @@ RCT_EXPORT_MODULE()
 }
 
 - (NSDictionary *)constantsToExport
+{
+  return [self getConstants];
+}
+
+- (NSDictionary *)getConstants
 {
   return @{@"initialAppState": RCTCurrentAppBackgroundState()};
 }

React/Modules/RCTDeviceInfo.m

@@ -104,6 +104,11 @@ static NSDictionary *RCTExportedDimensions(RCTBridge *bridge)
 }
 
 - (NSDictionary<NSString *, id> *)constantsToExport
+{
+  return [self getConstants];
+}
+
+- (NSDictionary<NSString *, id> *)getConstants
 {
   return @{
     @"Dimensions": RCTExportedDimensions(_bridge),

React/Modules/RCTI18nManager.m

@@ -33,6 +33,11 @@ RCT_EXPORT_METHOD(swapLeftAndRightInRTL:(BOOL)value)
 }
 
 - (NSDictionary *)constantsToExport
+{
+  return [self getConstants];
+}
+
+- (NSDictionary *)getConstants
 {
   return @{
     @"isRTL": @([[RCTI18nUtil sharedInstance] isRTL]),

React/Modules/RCTSourceCode.m

@@ -21,6 +21,11 @@ RCT_EXPORT_MODULE()
 }
 
 - (NSDictionary<NSString *, id> *)constantsToExport
+{
+  return [self getConstants];
+}
+
+- (NSDictionary<NSString *, id> *)getConstants
 {
   return @{
     @"scriptURL": self.bridge.bundleURL.absoluteString ?: @"",

React/Modules/RCTUIManager.m

@@ -1494,6 +1494,11 @@ static NSMutableDictionary<NSString *, id> *moduleConstantsForComponent(
 }
 
 - (NSDictionary<NSString *, id> *)constantsToExport
+{
+  return [self getConstants];
+}
+
+- (NSDictionary<NSString *, id> *)getConstants
 {
   NSMutableDictionary<NSString *, NSDictionary *> *constants = [NSMutableDictionary new];
   NSMutableDictionary<NSString *, NSDictionary *> *directEvents = [NSMutableDictionary new];