Handle op-limits (e.g. \oint) in KaTeX

[gnprice]

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

"""

514 messages failed because of unsupported css class: op-limits.

This seems to be used to align some elements in the center.

.op-limits {
    > .vlist-t {
        text-align: center;
    }
}

This should be straightforward to implement.
"""

If I understand correctly, an example where this appears is $$ \oint $$ ($$\oint$$), with the circle centered over the integral sign.

This was the 5th item after all the functionality included in releases so far (#46 (comment)).