Split EventDispatcher into interface and impl

[ejanzer]

Summary:
Creating an interface for EventDispatcher so I can implement it from a dummy/no-op EventDispatcher to use in bridgeless mode when the instance isn't alive.

Changelog: [Android] [Changed] Renamed EventDispatcher to EventDispatcherImpl and created EventDispatcher interface; calls to EventDispatcher contstructor need to be updated

Reviewed By: makovkastar

Differential Revision: D21695401

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D21695401

[pull-bot]

	Messages
📖	📋 Missing Changelog - Can you add a Changelog? To do so, add a "## Changelog" section to your PR description. A changelog entry has the following format: [CATEGORY] [TYPE] - Message. Details CATEGORY may be: General iOS Android JavaScript Internal (for changes that do not need to be called out in the release notes) TYPE may be: Added, for new features. Changed, for changes in existing functionality. Deprecated, for soon-to-be removed features. Removed, for now removed features. Fixed, for any bug fixes. Security, in case of vulnerabilities. MESSAGE may answer "what and why" on a feature level. Use this to briefly tell React Native users about notable changes.
📖	📋 Missing Test Plan - Can you add a Test Plan? To do so, add a "## Test Plan" section to your PR description. A Test Plan lets us know how these changes were tested.
📖	📋 Missing Summary - Can you add a Summary? To do so, add a "## Summary" section to your PR description. This is a good place to explain the motivation for making this change.

Generated by 🚫 dangerJS against 8f573ab

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
ios	-	universal	809,568	0

Base commit: ae7df2d

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	6,780,718	96
android	hermes	armeabi-v7a	6,442,968	106
android	hermes	x86	7,165,834	77
android	hermes	x86_64	7,056,521	96
android	jsc	arm64-v8a	8,948,503	77
android	jsc	armeabi-v7a	8,603,150	111
android	jsc	x86	8,776,758	107
android	jsc	x86_64	9,353,043	82

Base commit: ae7df2d

[react-native-bot]

This pull request was successfully merged by @ejanzer in 68c0edd.

^{When will my fix make it into a release? | Upcoming Releases}