Move kotlin to it's own file

kapt is going to make kotlin a little more complicated, move the
rules and tests to their own files.

Bug: 122251693
Test: m checkbuild
Change-Id: Ieed78b97995ced210b710bd50c357514cc8e3bc6
diff --git a/java/java.go b/java/java.go
index 7e82c59..d2710a8 100644
--- a/java/java.go
+++ b/java/java.go
@@ -974,7 +974,7 @@
 		flags.kotlincClasspath = append(flags.kotlincClasspath, deps.classpath...)
 
 		kotlinJar := android.PathForModuleOut(ctx, "kotlin", jarName)
-		TransformKotlinToClasses(ctx, kotlinJar, kotlinSrcFiles, srcJars, flags)
+		kotlinCompile(ctx, kotlinJar, kotlinSrcFiles, srcJars, flags)
 		if ctx.Failed() {
 			return
 		}