FIR: extends scope of SENSELESS_COMPARISON

FE1.0 only reports SENSELESS_COMPARISON if one of the operand is `null`.
This change makes FIR reports also in case one of the operand has type
`Nothing?`.

In addition, fix handling of type alias in ConeTypeContext#isNullableType

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnostics.kt

@@ -1825,7 +1825,7 @@ sealed class KtFirDiagnostic<PSI : PsiElement> : KtDiagnosticWithPsi<PSI> {
         abstract val unreachable: List<PsiElement>
     }
 
-    abstract class SenselessComparison : KtFirDiagnostic<KtBinaryExpression>() {
+    abstract class SenselessComparison : KtFirDiagnostic<KtExpression>() {
         override val diagnosticClass get() = SenselessComparison::class
         abstract val expression: KtExpression
         abstract val compareResult: Boolean

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnosticsImpl.kt

@@ -2944,7 +2944,7 @@ internal class SenselessComparisonImpl(
     override val compareResult: Boolean,
     firDiagnostic: FirPsiDiagnostic,
     override val token: ValidityToken,
-) : KtFirDiagnostic.SenselessComparison(), KtAbstractFirDiagnostic<KtBinaryExpression> {
+) : KtFirDiagnostic.SenselessComparison(), KtAbstractFirDiagnostic<KtExpression> {
     override val firDiagnostic: FirPsiDiagnostic by weakRef(firDiagnostic)
 }