Update IntelliSense docs to mention indexing and auto imports behaviours and settings

[luabud]

This PR is basically pulling information from this PR to our docs: https://github.com/microsoft/pylance-release/pull/3331

I tried to keep the specific details under each one of the settings, given settings references are more likely to be read by people who care about understanding each settings behaviour, and then left the overall explanation of the experience in the Editing page.

I also added a few settings that were missing and removed some outdated references (e.g. Pylance insiders setting).

[luabud]

@debonte @heejaechang @bschnurr if you could take a look and let me know if there's anything I added that is incorrect and/or there's any important info from https://github.com/microsoft/pylance-release/pull/3331 that I forgot to include here, it'd be super appreciated!

[luabud]

Once next week's Pylance release is out, we can merge this.