Use @react-native-communty/cli-plugin-metro project to bundling, and remove custom code in CLI and related packages

[afoxman]

I created @rnx-kit/metro-service from code in @react-native-community/cli to give us immediate access to calling Metro programmatically.

Check with @react-native-community/cli devs -- grabbou specifically -- about factoring out the code that talks to metro.

[afoxman]

The code I separated out of @react-native-community/cli is the buildBundle API and all subordinate APIs and types.

See /packages/cli/src/commands/bundle/buildBundle.ts.

[afoxman]

Talked with some people on discord including a maintainer, and I got the nod to go ahead with refactoring bundling & config code into separate cli packages.

• Move bundling command logic into /packages/cli-bundle-api and submit PR. There was an ask to focus on the asset logic and leave the bundling "command" where it is. This makes sense, but I need to review so I don't lose any logic.
• Once approved, submit fixes on top from the this PR
• Also, submit a PR which exposes the Metro config loader (and dependencies) into /packages/metro-config
• Once released/published, make use of both packages in our CLI

PR: react-native-community/cli#1447
@react-native-community/cli release version 6.1.0 includes the PR

[afoxman]

Still need to remove the custom code I added (copied) from @rnc community project. Now that it's all wrapped up and exposed through CLI, we should use that instead.

[tido64]

For future reference, @react-native-community/cli@6.1.0 is equivalent to react-native@0.66.

[kelset]

headsup: things have been moving around -> facebook/react-native#38795