Switch to using a normal <a href="..."> link for search result
clickthrough. Apart from generally giving a better experience, this means that
it also works on html messages. The problem there was that we were attaching
onClick handlers to <span>s which we were then flattening into HTML with
ReactDOMServer (which meant the onClick handlers were never attached to React's
list of listeners).
To make this work without jumping through React hoops, the highlighter now
returns either a list of strings or a list of nodes, depending on whether we
are dealing with an HTML event or a text one. We therefore have a separate
HtmlHighlighter and TextHighlighter.
matrix-js-sdk now retains redacted events. Filter them out of the timeline.
Also put empty placeholders in the dom so that if we try to scroll to a
redacted event, we don't end up blowing up.
This adds support for links to particular event ids: add /<eventId> to the URL
for a room.
This commit also ensures that we scroll to the 'read marker' when switching to
a room which has no previous scroll state, as well as preventing that marker
from going past the middle of the screen.
This also reinstates the preservation of scroll state when switching rooms,
which was disabled previously.
