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"<!>

compiler/testData/diagnostics/tests/modifiers/const/stringConcatenation.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 = <!NON_CONST_VAL_USED_IN_CONSTANT_EXPRESSION!>"A $nonConst B"<!>

compiler/testData/diagnostics/tests/modifiers/const/stringConcatenation.txt

@@ -0,0 +1,24 @@
+package
+
+public val nonConst: kotlin.Int = 0
+public const val printA: kotlin.String
+public const val printB: kotlin.String
+public const val simple: kotlin.String = "OK 3.0"
+public const val withInnerConcatenation: kotlin.String = "1 2 3 4 5 6"
+public const val withNonConst: kotlin.String = "A 0 B"
+public const val withNull: kotlin.String = "1 null"
+public const val withNullPlus: kotlin.String
+
+public object A {
+    private constructor A()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}
+
+public object B {
+    private constructor B()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ fun toString(): kotlin.String
+}