repoview: add a FilteredIndexError class This exception is a more precise IndexError that will allow us to issue a special message when we end up accessing a filtered revision.

changectx: move `IndexError` handling in the top level try except This one can be handled by the top level catching.

changectx: wrap the `changeid` processing in a try/except We are going to introduce more precise exception classes for filtered nodes. So we will have to upgrade them to the `RepoLookupError` level here. We wrap the whole thing into a try/except to ease this future catching. Some of the current exception catching will be moved in this one. But the current changeset focuses on code movement only.