Add ir interpreter tests

compiler/testData/ir/interpreter/proxy/customCharSequence.kt

@@ -0,0 +1,12 @@
+@CompileTimeCalculation
+class MyCharSequence(val str: String): CharSequence {
+    override val length: Int = str.length
+
+    override fun get(index: Int) = str[index]
+
+    override fun subSequence(startIndex: Int, endIndex: Int) = str.subSequence(startIndex, endIndex)
+}
+
+const val sbSize = StringBuilder(MyCharSequence("MyString")).<!EVALUATED: `8`!>length<!>
+const val appendSize = StringBuilder().append(MyCharSequence("MyString")).<!EVALUATED: `8`!>length<!>
+const val subSequenceSize = StringBuilder(StringBuilder(MyCharSequence("MyString")).subSequence(0, 4)).<!EVALUATED: `4`!>length<!>