fix(listview): update index after items removed

[TomJGooding]

Fixes #5114.

• The pop and remove_items methods now return AwaitComplete rather than AwaitRemove to account for the index update
• Previously trying to pop() from an empty list would raise a NoMatches error, this will now raise an IndexError for consistency.

Please review the following checklist.

• Docstrings on all new or modified functions / classes
• Updated documentation
• Updated CHANGELOG.md (where appropriate)

[TomJGooding]

I've now also updated the remove_items method, so hopefully I was on the right track!

[TomJGooding]

This now also reinstates always_update to the index reactive that was removed in recent changes. When items are removed, the index may not change but the highlighted item should be updated.

[willmcgugan]

I'd recommend against the always_update. Since it calls watchers you can get unintended side effects, such as re-sending messages.

Better to factor out the specific functionality you need and call it directly.

TBH I regret adding always_update. I know we've recommended it in the past, but this will rightly confuse anything not intimately familiar with reactives:

self.index = self.index

[willmcgugan]

Just a request for docstrings...

[willmcgugan]

Docstring and typing por favor. Since its internal, and essentially private, the docstrings can be written for future Textual core-devs.

[TomJGooding]

I've added docstrings in 9314cde, but feel free to tweak!

[willmcgugan]

docstrings please

[willmcgugan]

Hi Tom, is this ready to go?

[TomJGooding]

@willmcgugan If you're happy with my approach and the added tests cover all cases, I think this should be ready to go.

[darrenburns]

@willmcgugan I was going to merge, but it's blocked until you approve.