[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/testData/diagnostics/tests/enum/compareTwoDifferentEnums.txt

@@ -1,8 +1,11 @@
 package
 
 public fun jj(/*0*/ a: JavaEnumA, /*1*/ b: JavaEnumB): kotlin.Boolean
+public fun jj2(/*0*/ a: JavaEnumA, /*1*/ b: JavaEnumB): kotlin.Boolean
 public fun jk(/*0*/ a: JavaEnumA, /*1*/ b: KotlinEnumB): kotlin.Boolean
+public fun jk2(/*0*/ a: JavaEnumA, /*1*/ b: KotlinEnumB): kotlin.Boolean
 public fun kk(/*0*/ a: KotlinEnumA, /*1*/ b: KotlinEnumB): kotlin.Boolean
+public fun kk2(/*0*/ a: KotlinEnumA, /*1*/ b: KotlinEnumB): kotlin.Boolean
 
 public final enum class JavaEnumA : kotlin.Enum<JavaEnumA!> {
     public constructor JavaEnumA()