Missing space between sin and x

[runarberg]

Chrome and Firefox have a differing behavior when it comes to spacing between certain <mi> elements. Firefox adds a space between normal and italic <mi> elements, but Chrome doesn’t. For example sin x renders with a space between the function and variable in Firefox, but in chrome the variable is butted against the function.

A solution could be to add invisible function application (U+2061) between common functions identifiers and a variable that follows and give it an lspace of something like 0.35ex.

See https://github.com/w3c/mathml-core/issues/214