FIR: Fix incorrect type of block generated for inc operator

Previously, it was obtained from expected type of a variable being assigned,
but it's better to use the type of resulting expression

Initially this part was brought in 4ab0897d7d,
but as we see in commit message and tests it was all about unit-coercion

compiler/testData/diagnostics/tests/inference/completion/postponedArgumentsAnalysis/basic.fir.kt

@@ -155,7 +155,7 @@ fun main() {
     select(id(id(fun(x: String, y: String) { }), <!TOO_MANY_ARGUMENTS!>fun String.(x: String) {}<!>), { x, y -> x })
     val x26: Int.(String) -> Int = fun (x: String) = 10 // it must be error, see KT-38439
     // Receiver must be specified in anonymous function declaration
-    val x27: Int.(String) -> Int = id(<!ARGUMENT_TYPE_MISMATCH!>fun (x: String) = 10<!>)
+    val x27: Int.(String) -> Int = id(<!ARGUMENT_TYPE_MISMATCH, ARGUMENT_TYPE_MISMATCH!>fun (x: String) = 10<!>)
     select(id<Int.(String) -> Unit> {}, { x: Int, y: String -> x })
 
     // Inferring lambda parameter types by partially specified parameter types of other lambdas