[FIR] Resolve elvis call as special synthetic call

Before that commit we desugared `a ?: b` as

when (val elvis = a) {
    null -> b
    else -> elvis
}

It was incorrect, because `a` should be resolved in dependent mode,
  but when it was `elvis` initializer it was resolved in independent
  mode, so we can't infer type for `a` in some complex cases

compiler/testData/diagnostics/tests/inference/nothingType/discriminatedNothingAndSmartCast.fir.kt

@@ -15,5 +15,5 @@ fun test(s: String?, silent: Boolean) {
             throw Exception()
         }
 
-    s.<!INAPPLICABLE_CANDIDATE!>length<!>
+    s.length
 }

compiler/testData/diagnostics/tests/nullableTypes/uselessElvis.fir.kt

@@ -42,7 +42,7 @@ fun test() {
 inline fun <reified T : Any> reifiedNull(): T? = null
 
 fun testFrom13648() {
-    <!INAPPLICABLE_CANDIDATE!>takeNotNull<!>(reifiedNull() ?: "")
+    takeNotNull(reifiedNull() ?: "")
 }
 
 fun bar() = <!UNRESOLVED_REFERENCE!>unresolved<!>

compiler/testData/diagnostics/tests/resolve/specialConstructions/inferenceForElvis.fir.kt

@@ -3,6 +3,6 @@
 
 fun <T: Any> foo(f: (T) -> Unit): T? = null // T is used only as return type
 fun test() {
-    val x = foo { it checkType { <!INAPPLICABLE_CANDIDATE!>_<!><String>() }} ?: "" // foo() is inferred as foo<String>, which isn't very good
-    val y: Any = foo { it checkType { _<Any>() } } ?: "" // but for now it's fixed by specifying expected type
+    val x = foo { it checkType { _<String>() }} ?: "" // foo() is inferred as foo<String>, which isn't very good
+    val y: Any = foo { <!DEBUG_INFO_EXPRESSION_TYPE("kotlin.String")!>it<!> checkType { <!INAPPLICABLE_CANDIDATE!>_<!><Any>() } } ?: "" // but for now it's fixed by specifying expected type
 }