[native] Fix 'expo' command in nix env

Summary:
Analogous to D5508. I use the expo run:android instead of react-native run-android (see why) and it fails in Nix workflow. The solution is to do the same as in D5508.

I also added the run-ios and run-android scripts, because the COMM_DEV env should be provided when opening Metro bundler (and these commands do this unless already started or the --no-bundler flag is provided).

Test Plan:

• yarn dev still works the same way
• expo run:ios builds the native app successfully
• the same for expo run:android

Reviewers: ashoat, atul, jon

Reviewed By: ashoat, atul, jon

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D6309