[FIR] Report all Visibilities.Unknown in FirOverrideChecker

Check all members for `Visibility.Unknown`,
otherwise we miss them when they come
from supertypes. This is the reason why
the FP intellij build failed with a
cryptic stacktrace instead of a
human-readable diagnostic.

Also, do report the diagnostic at all
cases of `Visibilities.Unknown`. Turns
out, there are no "simple to reason
about" situations here :(

Also, an interesting detail:
`retrieveDirectOverriddenOf` returns an
empty list for intersection overrides.
But this doesn't seem to break anything...

Replacing `CANNOT_INFER_VISIBILITY`'s
type `KtDeclaration` with
`PsiNameIdentifierOwner` and the related
changes in `PositioningStrategies`
were needed to prevent an exception saying that
`PsiClassImpl` is not a subtype of
`KtDeclaration`.

compiler/testData/diagnostics/tests/intersectionWithMultipleDefaultsInJava.fir.kt

@@ -0,0 +1,34 @@
+// TARGET_BACKEND: JVM
+
+// FILE: IntCollection.java
+interface IntCollection<E> {
+    public boolean add(int key);
+}
+
+// FILE: IntSet.java
+interface IntSet extends IntCollection {
+    public default boolean add(Integer it) { return true; }
+
+    // from the supertype
+    // public boolean add(int key);
+}
+
+// FILE: AbstractCollection.java
+abstract class AbstractCollection<E> {
+    public boolean add(E it) { return true; }
+}
+
+// FILE: AbstractIntCollection.java
+abstract class AbstractIntCollection extends AbstractCollection<Integer> {
+    public boolean add(int it) { return true; }
+
+    // from the supertype
+    // public default boolen add(Integer it) { return true; }
+}
+
+// FILE: AbstractIntSet.java
+public abstract class AbstractIntSet extends AbstractIntCollection implements IntSet {}
+
+// FILE: Main.kt
+
+<!CANNOT_INFER_VISIBILITY!>class KotlinClass<!> : AbstractIntSet()