Minor: rename and refactor contract-related PSI checks in ktPsiUtil

compiler/psi/src/org/jetbrains/kotlin/psi/psiUtil/ktPsiUtil.kt

@@ -293,17 +293,20 @@ inline fun <reified T : KtElement, R> flatMapDescendantsOfTypeVisitor(
 
 // ----------- Contracts -------------------------------------------------------------------------------------------------------------------
 
-fun fastCheckIfContractPresent(element: KtElement): Boolean {
-    if (!isContractAllowedHere(element)) return false
-    val firstExpression = ((element as? KtFunction)?.bodyExpression as? KtBlockExpression)?.statements?.firstOrNull() ?: return false
-    return isContractDescriptionCallFastCheck(firstExpression)
+fun KtElement.isContractPresentPsiCheck(): Boolean {
+    val contractAllowedHere = this is KtNamedFunction &&
+            isTopLevel &&
+            hasBlockBody() &&
+            !hasModifier(KtTokens.OPERATOR_KEYWORD)
+    if (!contractAllowedHere) return false
+
+    val firstExpression = ((this as? KtFunction)?.bodyExpression as? KtBlockExpression)?.statements?.firstOrNull() ?: return false
+
+    return firstExpression.isContractDescriptionCallPsiCheck()
 }
 
-private fun isContractAllowedHere(element: KtElement): Boolean =
-    element is KtNamedFunction && element.isTopLevel && element.hasBlockBody() && !element.hasModifier(KtTokens.OPERATOR_KEYWORD)
-
-fun isContractDescriptionCallFastCheck(expression: KtExpression): Boolean =
-    expression is KtCallExpression && expression.calleeExpression?.text == "contract"
+fun KtExpression.isContractDescriptionCallPsiCheck(): Boolean =
+    this is KtCallExpression && calleeExpression?.text == "contract"
 
 
 // ----------- Other -----------------------------------------------------------------------------------------------------------------------