Fix sharing callback doesn't get called on Android.

[HelloCore]

Fixes #606

Android ShareDialog callback doesn't work.

Used one FBActivityEventListener instance instead of multiple instances.

Previously, we have one FBActivityEventListener for each module, and each one has CallbackManager.
However, after sharing something, the first CallbackManager that got called will run this static callback (because we didn't register the callback to this manager), and make AppCall invalid.
As a result, the CallbackManager for sharing module won't get called, because it has already been cleared

Test Plan:

Could be tested with the share button on the example app.

Video here.

• Old Version
• New Version

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[janicduplessis]

Sorry about the delay on this, thanks for investigating this!