[FIR] Handle receiver types of extension methods when computing maximally specific types.

Test case (from testPrimitiveReceiver):

fun Short.foo() = 3
fun Int.foo() = 4

1::foo

compiler/testData/diagnostics/tests/callableReference/resolve/kt9601.fir.kt

@@ -1,15 +0,0 @@
-// !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_EXPRESSION
-
-open class A
-class B: A()
-
-fun A.foo() {}
-fun B.foo() {} // more specific
-
-fun bar(a: Any) {}
-fun bar(a: Int) {}  // more specific
-
-fun test() {
-    <!UNRESOLVED_REFERENCE!>B::foo<!>
-    ::bar
-}

compiler/testData/diagnostics/tests/callableReference/resolve/kt9601.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_PARAMETER -UNUSED_EXPRESSION
 
 open class A

compiler/testData/diagnostics/tests/callableReference/resolve/moreSpecificAmbiguousExtensions.fir.kt

@@ -9,13 +9,13 @@ fun IB.extFun(x: IA) {}
 
 fun test() {
     val extFun1 = IA::extFun
-    val extFun2 = IB::extFun
+    val extFun2 = <!UNRESOLVED_REFERENCE!>IB::extFun<!>
 }
 
 fun testWithExpectedType() {
     val extFun_AB_A: IA.(IB) -> Unit = IA::extFun
-    val extFun_AA_B: IA.(IA) -> Unit = IB::extFun
+    val extFun_AA_B: IA.(IA) -> Unit = <!UNRESOLVED_REFERENCE!>IB::extFun<!>
     val extFun_BB_A: IB.(IB) -> Unit = IA::extFun
     val extFun_BA_B: IB.(IA) -> Unit = IB::extFun
-    val extFun_BB_B: IB.(IB) -> Unit = IB::extFun
+    val extFun_BB_B: IB.(IB) -> Unit = <!UNRESOLVED_REFERENCE!>IB::extFun<!>
 }

compiler/testData/diagnostics/tests/callableReference/resolve/moreSpecificSimple.fir.kt

@@ -1,12 +0,0 @@
-// !CHECK_TYPE
-
-interface IA
-interface IB : IA
-
-fun IA.extFun() {}
-fun IB.extFun() {}
-
-fun test() {
-    val extFun = <!UNRESOLVED_REFERENCE!>IB::extFun<!>
-    <!INAPPLICABLE_CANDIDATE!>checkSubtype<!><IB.() -> Unit>(extFun)
-}

compiler/testData/diagnostics/tests/callableReference/resolve/moreSpecificSimple.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !CHECK_TYPE
 
 interface IA

compiler/testData/diagnostics/tests/callableReference/resolve/overloads.fir.kt

@@ -20,7 +20,7 @@ fun fas() {}
 fun fas(i: Int = 1) {}
 
 fun test() {
-    <!UNRESOLVED_REFERENCE!>B::foo<!> // todo KT-9601 Chose maximally specific function in callable reference
+    B::foo // todo KT-9601 Chose maximally specific function in callable reference
 
     B::bar checkType { _<KFunction1<B, Unit>>() }