Implement Non-Final 1.5 Extensions API (#699)

* Implement non-final 1.5 extensions API

* Bump lib version max

* Add visibility to preferences

* Add preference visibility

build.gradle.kts

@@ -37,6 +37,10 @@ subprojects {
             dependsOn("formatKotlin")
             kotlinOptions {
                 jvmTarget = JavaVersion.VERSION_1_8.toString()
+
+                freeCompilerArgs += listOf(
+                    "-Xcontext-receivers"
+                )
             }
         }