[FIR] Fix incorrect inference of return type of anonymous functions

Also remove incorrect subtype check checkers

Test unsafeVarianceInAliasedFunctionalType.kt started to fail because
  of KT-54894. This bug existed before, changes from this commit just
  unhided it (previously it was hidden because incorrect subtype check
  in `isSubtypeForTypeMismatch` which is used by FirFunctionReturnTypeMismatchChecker

compiler/testData/diagnostics/tests/FunctionReturnTypes.fir.kt

@@ -10,7 +10,7 @@ fun unitUnitReturn() : Unit {return Unit}
 fun test1() : Any = {<!RETURN_NOT_ALLOWED!>return<!>}
 fun test2() : Any = a@ {return@a 1}
 fun test3() : Any { return }
-fun test4(): ()-> Unit = { <!RETURN_NOT_ALLOWED!>return@test4<!> }
+fun test4(): ()-> Unit = { <!RETURN_NOT_ALLOWED, RETURN_TYPE_MISMATCH!>return@test4<!> }
 fun test5(): Any = l@{ return@l }
 fun test6(): Any = {<!RETURN_NOT_ALLOWED!>return<!> 1}
 

compiler/testData/diagnostics/tests/functionLiterals/missedTypeMismatch.fir.kt

@@ -11,8 +11,8 @@ fun main() {
 
     val a0: () -> Int = <!INITIALIZER_TYPE_MISMATCH!>fun(): String = "1"<!>
     val a1: () -> Int = <!INITIALIZER_TYPE_MISMATCH!>(fun() = "1")<!>
-    val a2: () -> Unit = (fun() = <!RETURN_TYPE_MISMATCH!>"1"<!>)
-    val a3: Unit = <!INITIALIZER_TYPE_MISMATCH!>(fun() = <!RETURN_TYPE_MISMATCH!>"1"<!>)<!>
+    val a2: () -> Unit = <!INITIALIZER_TYPE_MISMATCH!>(fun() = "1")<!>
+    val a3: Unit = <!INITIALIZER_TYPE_MISMATCH!>(fun() = "1")<!>
     val a4 = (fun() = "1")
     val a5 = (fun(): String = "1")
     val a6: () -> Int = (fun() = 1)
@@ -36,5 +36,5 @@ fun main() {
     val a18: () -> Int = <!INITIALIZER_TYPE_MISMATCH!>fun() {}<!>
     val a19: () -> () -> Int = <!INITIALIZER_TYPE_MISMATCH!>fun() = fun() {}<!>
     val a20: () -> () -> () -> Unit = fun() = fun() = {}
-    val a21: () -> () -> () -> Int = fun() = fun() = {}
+    val a21: () -> () -> () -> Int = <!INITIALIZER_TYPE_MISMATCH!>fun() = fun() = {}<!>
 }

compiler/testData/diagnostics/tests/generics/projectionsScope/unsafeVarianceInAliasedFunctionalType.fir.kt

@@ -0,0 +1,11 @@
+class Foo<out T>(val baz: Baz<T>)
+
+class Bar {
+    val foo: Foo<*> = TODO()
+
+    fun <T> bar(): Baz<T> {
+        return <!RETURN_TYPE_MISMATCH!>foo.baz<!>
+    }
+}
+
+typealias Baz<T> = (@UnsafeVariance T) -> Unit

compiler/testData/diagnostics/tests/generics/projectionsScope/unsafeVarianceInAliasedFunctionalType.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 class Foo<out T>(val baz: Baz<T>)
 
 class Bar {

compiler/testData/diagnostics/tests/regressions/kt352.fir.kt

@@ -14,7 +14,7 @@ class A() {
 
 //more tests
 val g : () -> Unit = { 42 }
-val gFunction : () -> Unit = fun(): Int = 1
+val gFunction : () -> Unit = <!INITIALIZER_TYPE_MISMATCH!>fun(): Int = 1<!>
 
 val h : () -> Unit = { doSmth() }