fix gradle setup

[dulmandakh]

Description

This PR removes Android Gradle Plugin use in android folder or RN module, so that it won't create conflicts if version mismatches. Then creates a root gradle project, build.gradle.kts at root folder, so we can use it with Android Studio.

Also removed buildToolsVersion because it's been deprecated a long ago.

Steps to verify

Still can be used as RN module as before, but to develop you need to open not android folder but root folder with Android Studio.

[dulmandakh]

@kadikraman please review and merge

[friederbluemle]

Hi @dulmandakh - With the Android Gradle plugin removed, we're no longer able to open the android folder in Android Studio, or build the project individually. Did you find a way around that?

[friederbluemle]

Okay sorry - I didn't see you moved the Gradle files into the root directory. Since Gradle files are only Android related, wouldn't it be better to keep them contained in the android folder? Just like everything iOS is in the ios folder. For all React Native project, I normally do xed ios && studio android. Now with the files moved, this is no longer possible.

I'm also still trying to understand what exactly the problem is with a nested Android Gradle plugin - It should not be used if it's not declared in the root of the project (i.e. included as a module by other projects).

[dulmandakh]

In the past, I had many conflicts by modules that trying to load different versions of Android Gradle Plugin, thus causing build failures. This PR tries to resolve the issue moving AGP outside of the module.

I too want to contain everything Android in android folder, but I found this. I would be more than happy if you bring alternate solution to table.

[friederbluemle]

@dulmandakh - Yes, makes total sense. I actually found an alternate solution that results in the same outcome, without moving any Gradle related files into the root of a project.

Essentially, it's just two lines, wrapping the Android Gradle plugin dependency in the buildscripts section:

if (project == rootProject) {
    // ... (dependency here)
}

With this, the dependency is only evaluated (and possibly downloaded) when the project is opened stand-alone (opening the android folder in Android Studio).

When a library project is included as a dependency, then rootProject will be the main application project. -> the statement will evaluate to false, skipping the potentially outdated Android Gradle plugin download.

I opened a PR with the alternative approach here, which also includes a bit more description: #384 Please check 🙏