[FIR] Forbid erroneous ===-checks

It was decided to forbid such comparisons,
as we know how `===` works. Also, added some more
test cases, just for comparison.

Reusing the proper `canHaveSubtypes()`
from `TypeUtils` prevents a breaking change
in:

- `comparingTripleWithPair.kt`
- `comparisonOfGenericInterfaceWithGenericClass.kt`

But it does lead to warnings
(instead of errors) in
`incompatibleEnumEntryClasses.kt`, which is an
unrelated mistake that will be fixed in the next
commit.

The refactoring in `canHaveSubtypes()` is purely
cosmetic - otherwise reading these conditions is hard
(and they don't fit my screen vertically).

^KT-62646
^KT-65541
^KT-57779

compiler/tests-spec/testData/diagnostics/notLinked/dfa/pos/6.fir.kt

@@ -585,7 +585,7 @@ fun case_29(x: Boolean) {
     if (false || false || false || false || y !== v) {
         val t = <!DEBUG_INFO_EXPRESSION_TYPE("<anonymous>?")!><!UNSAFE_IMPLICIT_INVOKE_CALL!>y<!>()<!>
 
-        if (z !== t || false) {
+        if (<!EQUALITY_NOT_APPLICABLE_WARNING!>z !== t<!> || false) {
             <!DEBUG_INFO_EXPRESSION_TYPE("<anonymous>?")!>t<!><!UNSAFE_CALL!>.<!>a
             <!DEBUG_INFO_EXPRESSION_TYPE("<anonymous>?")!>t<!><!UNSAFE_CALL!>.<!>equals(null)
             <!DEBUG_INFO_EXPRESSION_TYPE("<anonymous>?")!>t<!>.propT