Implement constant folding in the IR backend for JVM

The newly added pass folds the set of constant functions of the
current backend, plus IrBuiltIns.

compiler/testData/codegen/bytecodeText/stringOperations/primitiveToStringNotOptimizable.kt

@@ -0,0 +1,14 @@
+fun main(a: Boolean, b:Byte, c: Short, d: Int, e: Long, f: Float, g: Double, h: Char) {
+    a.toString()
+    b.toString()
+    c.toString()
+    d.toString()
+    e.toString()
+    f.toString()
+    g.toString()
+    h.toString()
+}
+
+/*Check that all "valueOf" are String ones and there is no boxing*/
+// 8 valueOf
+// 8 INVOKESTATIC java/lang/String.valueOf