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/CheckNotNull.java

@@ -0,0 +1,10 @@
+package test;
+
+import org.jetbrains.annotations.NotNull;
+
+public class CheckNotNull {
+
+    @NotNull
+    public String returnNotNull() { return "42"; }
+
+}