U+2218 Ring operator (\circ) is very small

[PhilippImhof]

Currently, the ring operator is very small. Size of operators has already been discussed in #39. See comparison between Fira Math (blue) and Latin Modern Math (red):

One negative side effect is that expressions like $30^\circ$ are barely readable:

There has been a discussion in #34 that one should not use ^\circ for degrees, and while I agree that one should use the correct symbol (i.e. U+00B0 DEGREE SIGN), we know that ^\circ has a long history and is widely used (I believe it was even used by siunitx in some versions).

I suggest making the circle operator a bit larger.

[stone-zeng]

I made this symbol too small because in Unicode TR25 it was categorized as "very small". But compared with other fonts, I think it's better to make it larger: