FIR: Get rid of PSI dependency in the :fir:resolve module

compiler/fir/tree/src/org/jetbrains/kotlin/fir/Utils.kt

@@ -56,3 +56,20 @@ fun <R : FirTypeRef> R.copyWithNewSourceKind(newKind: FirFakeSourceElementKind):
     } as R
 }
 
+/**
+ * Let's take `a.b.c.call()` expression as an example.
+ *
+ * This function allows to transform `SourceElement(psi = 'a')` to `SourceElement(psi = 'a.b.c')`
+ * ([stepsToWholeQualifier] should be = 2 for that).
+ *
+ * @receiver original source element
+ * @param stepsToWholeQualifier distance between the original psi and the whole qualifier psi
+ */
+fun FirSourceElement.getWholeQualifierSourceIfPossible(stepsToWholeQualifier: Int): FirSourceElement {
+    if (this !is FirRealPsiSourceElement<*>) return this
+
+    val qualifiersChain = generateSequence(psi) { it.parent }
+    val wholeQualifier = qualifiersChain.drop(stepsToWholeQualifier).first()
+
+    return wholeQualifier.toFirPsiSourceElement() as FirRealPsiSourceElement
+}