[FIR] Fix enhancement of FlexibleNullability and EnhancedNullability

- Add utilities to add new attribute to ConeAttributes
- Get rid of FlexibleNullability attribute (it can be easily inferred
    for any flexible type at any moment)
- Fix determining of EnhancedNullability attribute

compiler/testData/ir/irText/expressions/sam/samConversionToGeneric.fir.kt.txt

@@ -1,51 +1,52 @@
-fun test1(): J<String?> {
-  return local fun <anonymous>(x: String?): String? {
+fun test1(): J<@FlexibleNullability String?> {
+  return local fun <anonymous>(x: @FlexibleNullability String?): @FlexibleNullability String? {
     return x
   }
- /*-> J<String?> */
+ /*-> J<@FlexibleNullability String?> */
 }
 
-fun test2(): J<String?> {
-  return local fun <anonymous>(x: String): String? {
+fun test2(): J<@FlexibleNullability String?> {
+  return local fun <anonymous>(x: String): @FlexibleNullability String? {
     return x
   }
- /*-> J<String?> */
+ /*-> J<@FlexibleNullability String?> */
 }
 
 fun test3() {
-  return bar<String?>(j = local fun <anonymous>(x: String): String? {
+  return bar<@FlexibleNullability String?>(j = local fun <anonymous>(x: String): @FlexibleNullability String? {
     return x
   }
- /*-> J<String?>? */)
+ /*-> @FlexibleNullability J<@FlexibleNullability String?>? */)
 }
 
 fun test4(a: Any) {
   a as J<String> /*~> Unit */
-  bar<String?>(j = a /*as J<String> */)
+  bar<@FlexibleNullability String?>(j = a /*as J<String> */)
 }
 
 fun test5(a: Any) {
   a as Function1<String, String> /*~> Unit */
-  bar<String?>(j = a /*as Function1<String, String> */ /*-> J<String?>? */)
+  bar<@FlexibleNullability String?>(j = a /*as Function1<String, String> */ /*-> @FlexibleNullability J<@FlexibleNullability String?>? */)
 }
 
 fun <T : Any?> test6(a: Function1<T, T>) {
-  bar<T?>(j = a /*-> J<T?>? */)
+  bar<@FlexibleNullability T?>(j = a /*-> @FlexibleNullability J<@FlexibleNullability T?>? */)
 }
 
 fun <T : Any?> test7(a: Any) {
   a as Function1<T, T> /*~> Unit */
-  bar<T?>(j = a /*as Function1<T, T> */ /*-> J<T?>? */)
+  bar<@FlexibleNullability T?>(j = a /*as Function1<T, T> */ /*-> @FlexibleNullability J<@FlexibleNullability T?>? */)
 }
 
-fun test8(efn: @ExtensionFunctionType Function1<String, String>): J<String?> {
-  return efn /*-> J<String?> */
+fun test8(efn: @ExtensionFunctionType Function1<String, String>): J<@FlexibleNullability String?> {
+  return efn /*-> J<@FlexibleNullability String?> */
 }
 
 fun test9(efn: @ExtensionFunctionType Function1<String, String>) {
-  bar<String?>(j = efn /*-> J<String?>? */)
+  bar<@FlexibleNullability String?>(j = efn /*-> @FlexibleNullability J<@FlexibleNullability String?>? */)
 }
 
 fun test10(fn: Function1<Int, String>) {
-  bar2x<Int?>(j2x = fn /*-> J2X<Int?>? */)
+  bar2x<@FlexibleNullability Int?>(j2x = fn /*-> @FlexibleNullability J2X<@FlexibleNullability Int?>? */)
 }
+