Added hasScope api to easily verify if the scope already pushed before

[mondoktamas]

In some cases, I need to check if the scope that I'm trying to push has already been pushed before.
There is an option to do it by setting the onScopeChanged callback and managing the scope changes in a stack somewhere in my sources, but as GetIt already manages the list of scopes, I believe the new hasScope() API can be a better way to check it.

[mondoktamas]

@escamoteur could you please take a look?

[escamoteur]

Hmm, my first reaction is 'if you don't know if you have already pushed that scope then something in your code is wrong' using the existence of a scope to store information feels wrong to me.
that said why don't you just check if a certain type that is registered in that sope is already registered isRegistered is your friend for that?

[mondoktamas]

In my case it's important to know when I handle a deep link, so before I push the routes I need to build the scopes properly.
But probably I can use the isRegistered as well. It just seems to me more natural to check if the scope has been pushed then check some modules if registered, modules can be registered in different scopes.

Anyway, thanks for the reply. If you feel this PR does not make sense then i'll close it

[escamoteur]

Yeah, deeplinks can make is difficult and I don't see a reason not to add it. will wait for another fix before pushing to pub