Psi2Ir: Fold constants when generating IR

This is necessary to avoid stack overflow errors on large constant
expressions.

compiler/testData/ir/irText/declarations/kt29833.kt.txt

@@ -12,7 +12,7 @@ object Definitions {
     get
 
   val ktValue: String
-    field = super.#CONSTANT
+    field = "constant"
     get
 
 }

compiler/testData/ir/irText/declarations/kt29833.txt

@@ -19,7 +19,7 @@ FILE fqName:interop fileName:/Definitions.kt
     PROPERTY name:ktValue visibility:public modality:FINAL [val]
       FIELD PROPERTY_BACKING_FIELD name:ktValue type:kotlin.String visibility:private [final]
         EXPRESSION_BODY
-          GET_FIELD 'FIELD IR_EXTERNAL_JAVA_DECLARATION_STUB name:CONSTANT type:kotlin.String visibility:public [final,static]' type=kotlin.String origin=GET_PROPERTY
+          CONST String type=kotlin.String value="constant"
       FUN DEFAULT_PROPERTY_ACCESSOR name:<get-ktValue> visibility:public modality:FINAL <> ($this:interop.Definitions) returnType:kotlin.String
         correspondingProperty: PROPERTY name:ktValue visibility:public modality:FINAL [val]
         $this: VALUE_PARAMETER name:<this> type:interop.Definitions