Report error instead of assertion when property is used as operator

#KT-34857 fixed

compiler/testData/diagnostics/tests/kt34857.fir.kt

@@ -0,0 +1,8 @@
+// !LANGUAGE: +NewInference
+
+val Int.plusAssign: (Int) -> Unit
+    get() = {}
+
+fun main() {
+    1 <!PROPERTY_AS_OPERATOR!>+=<!> 2
+}

compiler/testData/diagnostics/tests/kt34857.kt

@@ -0,0 +1,8 @@
+// !LANGUAGE: +NewInference
+
+val Int.plusAssign: (Int) -> Unit
+    get() = {}
+
+fun main() {
+    1 <!PROPERTY_AS_OPERATOR!>+=<!> 2
+}

compiler/testData/diagnostics/tests/kt34857.txt

@@ -0,0 +1,4 @@
+package
+
+public val kotlin.Int.plusAssign: (kotlin.Int) -> kotlin.Unit
+public fun main(): kotlin.Unit