[ios] Propose to connect metro server programmatically

[Kudo]

Summary

nowadays, we could only specify metro server by either dev settings or building time ip.txt.
this pr adds a new way to specify metro server programmatically which makes rn launcher or testing more feasible.

Changelog

[Internal] [iOS] [Added] - Propose to connect metro server programmatically

Test Plan

just exposing a public interface for RCTPackagerConnection without much code change.
test to call this interface success locally.

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
ios	-	universal	n/a	--

Base commit: bc1e602

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	9,120,136	+0
android	hermes	armeabi-v7a	8,646,167	+0
android	hermes	x86	9,559,472	+0
android	hermes	x86_64	9,525,646	+0
android	jsc	arm64-v8a	10,762,843	+0
android	jsc	armeabi-v7a	9,680,136	+0
android	jsc	x86	10,797,582	+0
android	jsc	x86_64	11,405,270	+0

Base commit: bc1e602

[yungsters]

Not on Android? 😅

Oh, I see #31842 now. 😁

[facebook-github-bot]

@yungsters has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@yungsters merged this pull request in e2b5b65.