Before 2017, Zulip's manage streams and settings UIs were tab in the
same pane position as our current message feed and recent topics.
That original implementation was implemented using Bootstrap tabs;
while it hasn't been in use for years, we had a bunch of stale code
related to it leftover in this module.
For multi word stream names, searching for particular phrases, like
the entirety of any word in it, caused no space to show before and/or
after that word. For example, searching for `core` resulted in
`**core**team` (the space between `core` and `team` missing).
The cause of this bug was that the immediate container was `div` with
`display: flex` and so spaces at the ends of its immediate child
elements: text nodes and `strong` elements - were not respected. This
is fixed now by wrapping all the `description_html` text in a `span`
element (while the optional user_pill_context stays in another `span`
as before).
Because the typeahead.js list items are currently just text, a user's
full name and avatar should be displayed in `input_pill`. To use
`input_pill`, a separate Handlebars partial view was created to
provide a mandatory container (`<div class="pill-container">`) for
`input_pill` and a flex container (`<div class="search_list_item">`)
for vertically aligning the text.
The description of each suggestion (i.e `description_html`) is
rendered as raw HTML, so every special character (e.g. whitespace)
should be HTML-escaped. This enables highlighting the substring in
each search suggestion that matches the query.
Fixes: #20267