Add possibility to interpret and fold IrStringConcatenation expression

compiler/testData/diagnostics/tests/modifiers/const/stringConcatenation.fir.kt

@@ -0,0 +1,16 @@
+const val simple = "O${'K'} ${1.toLong() + 2.0}"
+const val withInnerConcatenation = "1 ${"2 ${3} ${4} 5"} 6"
+
+object A
+object B {
+    override fun toString(): String = "B"
+}
+
+const val printA = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>"A: $A"<!>
+const val printB = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>"B: $B"<!>
+
+const val withNull = "1 ${null}"
+const val withNullPlus = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>"1" + null<!>
+
+val nonConst = 0
+const val withNonConst = <!CONST_VAL_WITH_NON_CONST_INITIALIZER!>"A $nonConst B"<!>