Handle big operators in KaTeX

[gnprice]

From our TeX content survey, at #mobile-team > KaTeX survey results @ 💬, @rajveermalviya writes:

"""

1344 messages failed because of unsupported inline css property: position: relative.

From querying the corpus manually, this is always observed along with mop op-symbol classes and top inline style, on some symbol spans.
Also there was only one instance of position: relative inline style being constructed in KaTeX implementation, which confirms this.

So, this one should be straight forward to fix.
"""

This was the top item after all the functionality included in releases so far (#46 (comment)).