Begin to fix guest notifications

* Put the newest notifications at the top
* Have at most 1 notification toast, which is non-interactive,
  but focuses the notification panel on click, and auto-dismisses
  on a timer.

Scaffolding for guest members in channels

Release notes:
- You can now set channels to "public" which will allow anyone to join
and become a member. In a future release guests joining public channels
will have reduced permissions.

This PR introduces a new Inline Assistant feature "Retrieve Context", to
dynamically fill the content in your generation prompt based on relevant
results returned from the Semantic Search for the Prompt.

Release Notes:

- Introduce "Retrieve Context" button in Inline Assistant

* on opening a language server's logs, a new editor for server logs is
now created from `\n`-joined `VecDeque` elements instead of a buffer, as
before
* every `VecDeque` entry is a log line we receiver out of stderr or LSP
server, and their general amount is capped with `let
MAX_STORED_LOG_ENTRIES: usize = 2000;`
* currently opened editor with logs (`Editor::multi_line`) keeps getting
log lines appended and may get over this cap, but only last stored 2000
entries will be restored on reopen
* similarly, cap rpc message logs

Release Notes:

- Improved memory usage by storing less language LSP server and rpc logs

This way, we can retrieve channel invite notifications when
responding to the invites.