[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/declarations/kt45308.ir.txt

@@ -0,0 +1,22 @@
+Module: a
+FILE fqName:a fileName:/a.kt
+  TYPEALIAS name:A visibility:public expandedType:kotlin.String
+Module: b
+FILE fqName:b fileName:/b.kt
+  FUN name:foo visibility:public modality:FINAL <> (f:kotlin.Function0<kotlin.String{ a.A }>) returnType:kotlin.String{ a.A }
+    VALUE_PARAMETER name:f index:0 type:kotlin.Function0<kotlin.String{ a.A }>
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun foo (f: kotlin.Function0<kotlin.String{ a.A }>): kotlin.String{ a.A } declared in b'
+        CALL 'public abstract fun invoke (): R of kotlin.Function0 [operator] declared in kotlin.Function0' type=kotlin.String{ a.A } origin=INVOKE
+          $this: GET_VAR 'f: kotlin.Function0<kotlin.String{ a.A }> declared in b.foo' type=kotlin.Function0<kotlin.String{ a.A }> origin=VARIABLE_AS_FUNCTION
+Module: c
+FILE fqName:<root> fileName:/c.kt
+  FUN name:box visibility:public modality:FINAL <> () returnType:kotlin.String
+    BLOCK_BODY
+      RETURN type=kotlin.Nothing from='public final fun box (): kotlin.String declared in <root>'
+        CALL 'public final fun foo (f: kotlin.Function0<kotlin.String{ a.A }>): kotlin.String{ a.A } declared in b' type=kotlin.String{ a.A } origin=null
+          f: FUN_EXPR type=kotlin.Function0<kotlin.String{ a.A }> origin=LAMBDA
+            FUN LOCAL_FUNCTION_FOR_LAMBDA name:<anonymous> visibility:local modality:FINAL <> () returnType:kotlin.String{ a.A }
+              BLOCK_BODY
+                RETURN type=kotlin.Nothing from='local final fun <anonymous> (): kotlin.String{ a.A } declared in <root>.box'
+                  CONST String type=kotlin.String value="OK"