FIR: Fix overload resolution for some invoke cases

Namely, it's about the cases when there are multiple variable candidates
with the same priority and all of them should be collected and compared

compiler/fir/analysis-tests/testData/resolve/callResolution/invokeAmbiguity.kt

@@ -0,0 +1,17 @@
+open class A {
+    operator fun invoke(f: () -> Unit): Int = 1
+}
+
+class B {
+    operator fun invoke(f: () -> Unit): CharSequence = ""
+}
+
+open class C
+val C.attr: A get() = TODO()
+
+open class D: C()
+val D.attr: B get() = TODO()
+
+fun box(d: D) {
+    (d.attr {}).length
+}