Element-web: Add support for reading markdown tables

[tmdoit]

Format markdown table like in Mattermost clients: https://docs.mattermost.com/help/messaging/formatting-text.html#tables

[t3chguy]

riot-web does support tables just fine, the markdown flavour of choice does not support entering them though, feel free to open an issue with commonmark re tables, or upvote https://github.com/vector-im/riot-web/issues/5940 if you want to switch to GFM which supports them.

[dessalines]

This standard markdown table syntax doesn't seem to work in element:

a | table
--- | ---
a | row