[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/testsWithStdLib/comparingDifferentSubclassesCommonInterface.fir.kt

@@ -7,4 +7,7 @@ class B : I
 fun test(a: A, b: B) {
     a == b
     a == b as I
+
+    <!EQUALITY_NOT_APPLICABLE!>a === b<!>
+    a === b as I
 }

compiler/testData/diagnostics/testsWithStdLib/comparingDifferentSubclassesCommonInterface.kt

@@ -7,4 +7,7 @@ class B : I
 fun test(a: A, b: B) {
     <!EQUALITY_NOT_APPLICABLE!>a == b<!>
     a == b as I
+
+    <!EQUALITY_NOT_APPLICABLE!>a === b<!>
+    a === b as I
 }

compiler/testData/diagnostics/testsWithStdLib/comparingPlatformTypes.fir.kt

@@ -11,4 +11,7 @@ class A
 fun main(args: Array<String>) {
     (1 to A()) == A()
     (1 to B()) == B()
+
+    <!EQUALITY_NOT_APPLICABLE!>(1 to A()) === A()<!>
+    <!EQUALITY_NOT_APPLICABLE!>(1 to B()) === B()<!>
 }

compiler/testData/diagnostics/testsWithStdLib/comparingPlatformTypes.kt

@@ -11,4 +11,7 @@ class A
 fun main(args: Array<String>) {
     <!EQUALITY_NOT_APPLICABLE!>(1 to A()) == A()<!>
     <!EQUALITY_NOT_APPLICABLE!>(1 to B()) == B()<!>
+
+    <!EQUALITY_NOT_APPLICABLE!>(1 to A()) === A()<!>
+    <!EQUALITY_NOT_APPLICABLE!>(1 to B()) === B()<!>
 }

compiler/testData/diagnostics/testsWithStdLib/comparingTripleWithPair.fir.kt

@@ -7,4 +7,9 @@ fun test() {
     if (Triple(0, 1, 2) == Pair(Foo.A, "a")) println("Doesn't compile")
     if (Triple(0, 1, 2) == Pair("a", "b")) println("Doesn't compile")
     if (Triple(Foo.A, 1, 2) == Pair(Foo.A, "a")) println("Compiles, but why?")
+
+    <!EQUALITY_NOT_APPLICABLE!>Triple(Foo.A, 1, 2) === Pair("a", "b")<!>
+    <!EQUALITY_NOT_APPLICABLE!>Triple(0, 1, 2) === Pair(Foo.A, "a")<!>
+    <!EQUALITY_NOT_APPLICABLE!>Triple(0, 1, 2) === Pair("a", "b")<!>
+    <!EQUALITY_NOT_APPLICABLE_WARNING!>Triple(Foo.A, 1, 2) === Pair(Foo.A, "a")<!>
 }

compiler/testData/diagnostics/testsWithStdLib/comparingTripleWithPair.kt

@@ -7,4 +7,9 @@ fun test() {
     if (<!EQUALITY_NOT_APPLICABLE!>Triple(0, 1, 2) == Pair(Foo.A, "a")<!>) println("Doesn't compile")
     if (<!EQUALITY_NOT_APPLICABLE!>Triple(0, 1, 2) == Pair("a", "b")<!>) println("Doesn't compile")
     if (Triple(Foo.A, 1, 2) == Pair(Foo.A, "a")) println("Compiles, but why?")
+
+    <!EQUALITY_NOT_APPLICABLE!>Triple(Foo.A, 1, 2) === Pair("a", "b")<!>
+    <!EQUALITY_NOT_APPLICABLE!>Triple(0, 1, 2) === Pair(Foo.A, "a")<!>
+    <!EQUALITY_NOT_APPLICABLE!>Triple(0, 1, 2) === Pair("a", "b")<!>
+    Triple(Foo.A, 1, 2) === Pair(Foo.A, "a")
 }