I have opened android plugin of Firebase Auth but I cannot access flutter dependencies. What can I do to be able to use features like autocomplete?
When I run the code, everything works fine.
Alright, there is an easy solution for that!
Open Android studio and open the map viewer and make sure you are in the Project view.

Now create a new directory and call it something like tmplibs.

Alright, now navigate to your Flutter SDK directory. So where you cloned the Flutter repo. Then open the bin folder, after that the cache folder, followed by the artifacts folder, now open the engine folder and finally open the android-x64 folder.
So the path will look something like this:
...\flutter\bin\cache\artifacts\engine\android-x64
In here, you'll find a file called flutter.jar. Copy that and paste it in your new tmplibs folder!

Now right click on the flutter.jar file in project view in Android studio and click on Add As Library...

Finally click on Dependencies and changes the scope of tmplibs/flutter.jar to provided.

That's it!
A better solution is to use the android project of the example app instead of the library. See this issue response on github: https://github.com/flutter/flutter/issues/11632
Bram Vanbilsen's solution resolves the problem. But comment the implementation line in build.gradle file after building the plugin.
dependencies {
implementation files('tmplibs/flutter.jar')
}
If you run the example app without commenting the above line, it produces Duplicate dependencies error as the flutter source is included in the example app's build.gradle file.