[CommCoreModule] Add openSocket to CommCoreModuleSchema

Summary:
When initially trying to codegen openSocket, we ran into issues setting the return type to GRPCStream and decided to "generate" the code manually for the time being.

This was confusing for other members of the team as a chunk of the "generated" code would disappear when they tried to codegen "the right way."

Typing the openSocket return type as Object in CommCoreModuleSchema gets around this issue even if it isn't typed perfectly. We were returning a jsi::Object anyways, so this continues to work as expected.

[ignore: depends on D3123]

Test Plan: The GRPCStreamHostObject functionality continued to work as expected

Reviewers: ashoat, def-au1t, varun, palys-swm

Reviewed By: ashoat, varun, palys-swm

Subscribers: Adrian, karol-bisztyga, benschac

Differential Revision: https://phabricator.ashoat.com/D3125