Localization with FCM Admin (Node.js)

[maxtomczyk]

Use params allowed for localization by FCM Admin module for Node.js. This pull requests is for Android only, I can't develop it for iOS currently.

Description

Modified localizeKey and nomalizeExtras (FCMService.java) to correctly handle localization params allowed by official FCM Admin package. Added new constants (PushConstants.java)

Related Issue

#2435

Motivation and Context

fcm-node package is depracated and this plugin needs client side message localization capability.

How Has This Been Tested?

Sending requests to FCM as shown in example in docs.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.