Ensure key name uniqueness (#3641)

Fixes #3639

(cherry picked from commit 45e4cb1)

Author: roji

src/EFCore.PG/Metadata/Conventions/NpgsqlSharedTableConvention.cs

@@ -24,6 +24,18 @@ protected override bool AreCompatible(IReadOnlyIndex index, IReadOnlyIndex dupli
         => base.AreCompatible(index, duplicateIndex, storeObject)
             && index.AreCompatibleForNpgsql(duplicateIndex, storeObject, shouldThrow: false);
 
+    /// <inheritdoc />
+    protected override bool KeysUniqueAcrossTables
+        => true;
+
+    /// <inheritdoc />
+    protected override bool ForeignKeysUniqueAcrossTables
+        => false;
+
+    /// <inheritdoc />
+    protected override bool IndexesUniqueAcrossTables
+        => true;
+
     /// <inheritdoc />
     protected override bool CheckConstraintsUniqueAcrossTables
         => false;