[FIR] Properly calculate visibilities

`testIntersectionOfPrimitiveBasedFunctions`
is fine, because we deprecate this
already in ^KT-63243.

`CANNOT_INFER_VISIBILITY` is
positioned as `DECLARATION_NAME`,
just in case we decide for
some reason that we do want to
report it along with
`MANY_*_NOT_IMPLEMENTED`. In that
case, we'd get a problem that
their bounds overlap, but not
completely contain one another.

^KT-63741 Fixed
^KT-59400 Fixed

compiler/fir/semantics/src/org/jetbrains/kotlin/fir/EffectiveVisibilityUtils.kt

@@ -37,6 +37,10 @@ fun Visibility.toEffectiveVisibility(
         }
         Visibilities.Public -> EffectiveVisibility.Public
         Visibilities.Local -> EffectiveVisibility.Local
+        // Unknown visibility should not provoke errors,
+        // because they can naturally appear when intersection
+        // overrides' bases have inconsistent forms.
+        Visibilities.Unknown -> EffectiveVisibility.Unknown
         else -> errorWithAttachment("Unknown visibility: $this") {
             withFirLookupTagEntry("owner", owner)
         }