Improve inference on generics for callable references

#KT-10711 Fixed
 #KT-12802 Fixed
 #KT-12964 Fixed
 #KT-15439 Fixed

Analyze callable references in `dependent` mode, then complete them with
respect to expected types

compiler/testData/diagnostics/tests/callableReference/generic/specialCalls.kt

@@ -0,0 +1,23 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER, -UNUSED_VARIABLE
+
+fun baz(i: Int) = i
+fun <T> bar(x: T): T = TODO()
+
+fun nullableFun(): ((Int) -> Int)? = null
+
+fun test() {
+    val x1: (Int) -> Int = bar(if (true) ::baz else ::baz)
+    val x2: (Int) -> Int = bar(nullableFun() ?: ::baz)
+    val x3: (Int) -> Int = bar(::baz <!USELESS_ELVIS!>?: ::baz<!>)
+
+    val i = 0
+    val x4: (Int) -> Int = bar(when (i) {
+                                   10 -> ::baz
+                                   20 -> ::baz
+                                   else -> ::baz
+                               })
+
+    val x5: (Int) -> Int = bar(::baz<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>)
+
+    (if (true) ::baz else ::baz)(1)
+}