[FIR] Utilize equality compatibility logic for cast checks

This makes it more consistent and fixes some
overlooked corner cases. Also it was decided
on the last equality applicability DM
(KT-62646) that we'd like
`is`/`!is`/`as`/`as?` to work similarly
to `===`/`!==`.

Also note that it now gives a clearer
explaination of why some corner cases work
the way they do. For example,
`FirPsiDiagnosticTestGenerated.testLambdaInLhsOfTypeOperatorCall`
yields `UNCHECKED_CAST` instead of
`CAST_NEVER_SUCCEEDS`, because
`toTypeInfo()` replaces all type arguments
with star projections, even when the argument
is not a type parameter. This is because
it has been desided to work this way in
KT-57779.

In
`FirPsiOldFrontendDiagnosticsTestGenerated..NeverSucceeds#testNoGenericsRelated`
the diagnostic is introduced, because
`t2 as FC1` and `FC1` is a final class with
no `T5` supertype.

`UNCHECKED_CAST` in
`FirPsiOldFrontendDiagnosticsTestGenerated.testSmartCast`
disappeared, because previously we didn't
take smartcasts into account.

Note that
`FirPsiOldFrontendDiagnosticsTestGenerated.testMappedSubtypes`
is a false positive. It appears because `isSubtypeOf()` doesn't
take into account platform types in supertypes of the given types
(doesn't map them).

compiler/fir/analysis-tests/testData/resolve/lambdaInLhsOfTypeOperatorCall.kt

@@ -9,7 +9,7 @@ fun test_1(b: B<String, Number>) {
 }
 
 fun test_2(s: String) {
-    val func = { s.length } <!UNCHECKED_CAST!>as B<Int, Int><!>
+    val func = { s.length } <!CAST_NEVER_SUCCEEDS!>as<!> B<Int, Int>
 }
 
 class B<out K, V>(val k: K, val v: V)

compiler/fir/analysis-tests/testData/resolve/smartcasts/receivers/implicitReceivers.kt

@@ -79,6 +79,6 @@ fun Any.test_5(): Int = when {
 fun Any.test_6() {
     this as List<*>
     size
-    this as String
+    this <!CAST_NEVER_SUCCEEDS!>as<!> String
     length
 }