Currently the only two ways to spoiler text in your message is either:
* Using the /spoiler command
* Manually typing the data-mx-spoiler span HTML blocks
Neither one is discoverable, or friendly to users really. Instead, we
should extend our existing Markdown-based formatting syntax with one
that can handle spoiler tags. I chose the || syntax to match Discord,
since Element doesn't seem to adopt one.
Unfortunately, CMark does not support custom extensions (see
https://github.com/commonmark/cmark/pull/123) so we have to implement
our own parsing function. New tests are also added for this too.
This is because we only check if the last message component != Text,
because that handles it's own edit strings. Quote components do that
too, so if we don't exclude it there ends up being two (edited) strings
in one message.
This was a mistake in the code that was designed to remove the outside
paragraphs, which seems to be to make way for the quotation marks we
add around the text. Instead of doing that (which turns out, is very
brittle and breaks on multiple paragraphs) insert the quotation marks
*inside* of the paragraph tags.
A test case is added for this as well.
