[FIR] Save IR dumps to .ir.txt files instead of .txt in tests

This is needed to avoid clashes between different dumps from different
  handlers

compiler/testData/ir/irText/expressions/genericPropertyRef.kt.txt

@@ -17,13 +17,13 @@ class Value<T : Any?> {
 
 }
 
-val <T : Any?> Value<T>.additionalText: Int /* by */ 
+val <T : Any?> Value<T>.additionalText: Int /* by */
   field = DVal(kmember = Value::text)
   get(): Int {
     return #additionalText$delegate.getValue(t = <this>, p = ::additionalText/*<T>()*/)
   }
 
-val <T : Any?> Value<T>.additionalValue: Int /* by */ 
+val <T : Any?> Value<T>.additionalValue: Int /* by */
   field = DVal(kmember = Value::value)
   get(): Int {
     return #additionalValue$delegate.getValue(t = <this>, p = ::additionalValue/*<T>()*/)
@@ -68,4 +68,3 @@ var <T : Any?> T.bar: T
 val barRef: KMutableProperty1<String?, String?>
   field = ::bar/*<String?>()*/
   get
-