Load custom RCTURLRequestHandler dynamically.

[cipolleschi]

Summary: Libraries can declare their own objects and modules that can conform to RCTURLRequestHandler. The new architecture has no mechanism to load those custom classes.

This change is a proposal on how this can be achieved in a declarative way, by leveraging codegen.

If users want to opt-out from codegen, they can update the RCTURLRequestHandlerProvider.mm manually.

Changelog:

[iOS][Added] - Offer mechanism to link custom RCTURLHandler when the app starts

Differential Revision: D53312017

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D53312017

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D53312017