Double-encoding of HTML entities in certain chat messages

[jpd236]

The chat message renderer uses marked.lexer to tokenize Markdown chat messages; in some cases, we reference the resulting token.text field to obtain just the text and render it inside an HTML tag. We then have our own rendering logic. However, as noted at markedjs/marked#1737, the lexer will encode HTML entities, rather than leaving that to the renderer. React applies its own encoding for dynamic content, which results in double-encoding.

For example, sending a code block (inside backticks) with an apostrophe inside the code will result in the user-visible message containing the HTML entity for apostrophe.

We can fix this by decoding the output of marked.lexer whenever it is used.