Split GitHub provider out into its own module

[SUPERCILEX]

Fixes #1389 and #1412

[samtstern]

Mostly LGTM! Just some very small comments.

Also do you think this means we need to go to 5.0.0?

I kinda wanted to save v5 for something cool but I guess I am being overly sentimental about versioning.

[samtstern]

Should this be in .github.data.remote just to be consistent?

[samtstern]

Any particular reason to kill these comments?

[SUPERCILEX]

Our documentation in the config.xml is different in the auth vs app module, so I was trying to unify them. I've made it so auth is the documented one with app pointing to it. WDYT? Should it be flipped?

[SUPERCILEX]

Regarding 5.0, I don't think so? Everything will still compile as before, it'll "just" be a runtime crash. I don't think we need to bump to 5.0 because people have to update their deps anyway to get this change (so it's not super hard to add another dep).

I am being overly sentimental about versioning

🤣

TODO(me):

• Check release builds
• Update documentation

[samtstern]

Ok two questions about this string:

1. I see we have duplicate strings.xml entries for firebase_web_host in both auth/.../strings.xml and auth-github/.../strings.xml ... is there a reason it needs to exist outside of the GitHub module? I feel like we only use it there but could be forgetting something.
2. Now that we're sure you want to use GitHub auth when you include the -github module, should we explode at runtime if this string is still equal to CHANGE-ME? I think that might be helpful.

[SUPERCILEX]

Yup, both those birds were killed with the same stone in the original implementation 😁:

FirebaseUI-Android/auth/src/main/java/com/firebase/ui/auth/AuthUI.java

Lines 973 to 977 in f83c621

	Preconditions.checkConfigured(getApplicationContext(),
	"GitHub provider unconfigured. Make sure to add your client id and secret." +
	" See the docs for more info:" +
	" https://github.com/firebase/FirebaseUI-Android/blob/master/auth/README.md#github",
	R.string.firebase_web_host,

1. We need firebase_web_host in the auth module to do that check
2. We do that check 😂

[samtstern]

D'oh

[samtstern]

Did something change about how Facebook uses custom tabs?

[SUPERCILEX]

Nope, but we use custom tabs ourselves (for the ToS and PP) so it was a duplicate dependency:

FirebaseUI-Android/auth/build.gradle.kts

Line 25 in df554e2

implementation(Config.Libs.Support.customTabs)