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/Singleton.txt

@@ -0,0 +1,13 @@
+package test
+
+public fun getSingleton(): test.Singleton!
+public fun getString(): kotlin.String!
+
+public final class Singleton {
+    private constructor Singleton()
+
+    // Static members
+    private final var INSTANCE: test.Singleton!
+    public open fun getInstance(): test.Singleton!
+    public open fun getString(): kotlin.String!
+}