FIR checker: fix position strategy for UNRESOLVED_LABEL

compiler/testData/diagnostics/tests/thisAndSuper/QualifiedThis.fir.kt

@@ -2,11 +2,11 @@
 class A() {
   fun foo() : Unit {
     this@A
-    <!UNRESOLVED_LABEL!>this@a<!>
+    this<!UNRESOLVED_LABEL!>@a<!>
     this
   }
 
   val x = this@A.foo()
   val y = this.foo()
   val z = foo()
-}
+}

compiler/testData/diagnostics/tests/thisAndSuper/thisInFunctionLiterals.fir.kt

@@ -11,8 +11,8 @@ class A(val a:Int) {
         checkSubtype<A>(this@A)
       }
       val b: Double.() -> Unit = a@{ checkSubtype<Double>(this@a) + checkSubtype<Byte>(this@xx) }
-      val c = a@{ -> <!UNRESOLVED_LABEL!>this@a<!> + checkSubtype<Byte>(this@xx) }
+      val c = a@{ -> this<!UNRESOLVED_LABEL!>@a<!> + checkSubtype<Byte>(this@xx) }
       return (a@{checkSubtype<Double>(this@a) + checkSubtype<Byte>(this@xx)})
     }
   }
-}
+}

compiler/testData/diagnostics/tests/thisAndSuper/thisInPropertyInitializer.fir.kt

@@ -3,6 +3,6 @@ interface Base {
 }
 val String.test: Base = <!EXTENSION_PROPERTY_WITH_BACKING_FIELD!>object<!>: Base {
     override fun foo() {
-        <!UNRESOLVED_LABEL!>this@test<!>
+        this<!UNRESOLVED_LABEL!>@test<!>
     }
-}
+}

compiler/testData/diagnostics/tests/thisAndSuper/thisInToplevelFunction.fir.kt

@@ -1,4 +1,4 @@
 fun foo1() : Unit {
   <!NO_THIS!>this<!>
-  <!UNRESOLVED_LABEL!>this@a<!>
-}
+  this<!UNRESOLVED_LABEL!>@a<!>
+}