Introduce experimental -Xuse-javac compilation mode

In this mode, javac AST and Symbol files are used during
Kotlin compilation instead of PSI / binary stuff.
Later, they are reused for Java file compilation.
javac in this mode is integrated into kotlinc.

compiler/testData/compileKotlinAgainstJava/Vararg.txt

@@ -0,0 +1,10 @@
+package test
+
+public fun useVarargs(): kotlin.Unit
+
+public open class Vararg {
+    public constructor Vararg()
+
+    // Static members
+    public open fun method(/*0*/ vararg kotlin.String! /*kotlin.Array<(out) kotlin.String!>!*/): kotlin.Unit
+}