[gradle] Add a customization for resources directories.

[terrakok]

With the new API it is possible to customize compose resources directories. For example:

abstract class GenerateAndroidRes : DefaultTask() {
    @get:Inject
    abstract val layout: ProjectLayout

    @get:OutputDirectory
    val outputDir = layout.buildDirectory.dir("generatedAndroidResources")

    @TaskAction
    fun run() {...}
}
compose.resources {
    customDirectory(
        sourceSetName = "androidMain",
        directoryProvider = tasks.register<GenerateAndroidRes>("generateAndroidRes").map { it.outputDir.get() }
    )
    customDirectory(
        sourceSetName = "desktopMain",
        directoryProvider = provider { layout.projectDirectory.dir("desktopResources") }
    )
}

Fixes #4718
Fixes #4564

Release Notes

Features - Resources

• Add a customization for resources directories. Now it is possible to use e.g downloaded resources.

[igordmn]

The new API looks good to me