Setting the `defaultlocale` should update developmentRegion and knownRegions in pbxproj

# Feature Request

## Motivation Behind Feature

Since #237 adding a `defaultlocale="XX"` attribute to the `widget` tag in _config.xml_ allows to set the `CFBundleDevelopmentRegion` to a different language (in the _-Info.plist_ file).

⇒ This same language should also be applied into the pbxproj files of the project and CordovaLib, to replace the hardcoded `en` from the templates for `developmentRegion` and `knownRegions`.

## Feature Description

The templates for the project and CordovaLib are used to init the iOS project structure.

With previous #237, the [\_\_PROJECT_NAME\_\_-Info.plist](https://github.com/apache/cordova-ios/blob/master/templates/project/__PROJECT_NAME__/__PROJECT_NAME__-Info.plist) file is modified to target `CFBundleDevelopmentRegion` and replace the hardcoded value of [`en_US`](https://github.com/apache/cordova-ios/blob/master/templates/project/__PROJECT_NAME__/__PROJECT_NAME__-Info.plist#L6) with the language set through `defaultlocale`.

Same should be done in [project pbxproj](https://github.com/apache/cordova-ios/blob/master/templates/project/__PROJECT_NAME__.xcodeproj/project.pbxproj) file and [CordovaLib pbxproj](https://github.com/apache/cordova-ios/blob/master/CordovaLib/CordovaLib.xcodeproj/project.pbxproj) file, targeting [`developmentRegion`](https://github.com/apache/cordova-ios/blob/master/templates/project/__PROJECT_NAME__.xcodeproj/project.pbxproj#L236) ([+](https://github.com/apache/cordova-ios/blob/master/CordovaLib/CordovaLib.xcodeproj/project.pbxproj#L507)) and [`knownRegions`](https://github.com/apache/cordova-ios/blob/master/templates/project/__PROJECT_NAME__.xcodeproj/project.pbxproj#L238) ([+](https://github.com/apache/cordova-ios/blob/master/CordovaLib/CordovaLib.xcodeproj/project.pbxproj#L509)) and replacing the hardcoded value of `en` there too.

~(may require https://github.com/apache/cordova-node-xcode/issues/122?)~

## Alternatives or Workarounds

Custom script after platform add.

Or should I start a new cordova-plugin to add more defaults like this about locales? (to include this, https://github.com/apache/cordova-android/issues/1396, https://github.com/kelvinhokk/cordova-plugin-localization-strings/issues/65, and more?)

Start with templates/project/__PROJECT_NAME__.xcodeproj/project.pbxproj and CordovaLib/CordovaLib.xcodeproj/project.pbxproj, then trace how they are populated during iOS project initialization. Verify that defaultlocale from config.xml replaces the hardcoded en in developmentRegion and knownRegions in both generated pbxproj files.

Written by the indexing model from the issue text.