Add aar support when importing sbt-android

[pfn]

Implemented by:

• change extractProject to return Seq[ProjectData]
• adding a new Aar data type which contains a synthetic ProjectData which contains synthetic AndroidData for the aar module
• inspecting the aars task in sbt-android and mapping aar values to the Aar data type
• when running extractProject inspect android for any aar values and expand them to a list

[pfn]

@jastice for review, and maybe @pavelfatin and @Alefas

[jastice]

I manually merged and adapated this PR due to conflicting changes: https://github.com/JetBrains/sbt-structure/tree/pfn-aar-support

Can you check if everything works as expected for you? (The Android tests are not adapted yet)

[pfn]

changes on pfn-aar-support look good, tests ok on my end.

Before merging this in, my main question to you: is this a good approach for handling these aar modules? does the android plugin in intellij have anything special to handle aar differently that can be leveraged?

[jastice]

Good question. I am not familiar with anything Android-related but I'll ask around. We can probably take this change as is and adapt the support later.

[jastice]

From @alexruiz:

The specific part of AARs is in the class com.android.tools.idea.gradle.project.sync.setup.module.dependency.Dependency
It is a little too long to paste here, but the code deals with AndroidModuleModel and BaseArtifact, which are the holders of dependencies in the Android model