Follow-up task to T375974 with other minor problems related to operators.
See https://www.mediawiki.org/wiki/Extension:Math/Native_MathML/Operators
- `<math>B * C \ast D</math>` the rendering of * and \ast is different in mathml, but not in SVG. Case 12e
- `<math>A \setminus B \smallsetminus B \times C</math>` \setminus and \smallsetminus render differently in SVG, but not in MathML. Case 12l
- `<math>A \nsubseteqq B \nsupseteqq C</math>` render differently, in SVG and MthML. Cases 12q and 12r
- `<math>A := B</math>` space added between : and = in MathML mode bug T401746, case 12t
- `<math>E \nleq F \nleqq G</math>` both operators render identically in MathML but differ in SVG, case 12y
- `<math>E \ngeq F \ngeqq G</math>` both operators render identically in MathML but differ in SVG, case 12z
- `<math>A \parallel B \nparallel B \shortparallel B \nshortparallel C</math>` short versions are shorter in SVG but same size in MathML
- `<math>A \ulcorner B \urcorner B \llcorner B \lrcorner C</math>` more spaces around operators in MathML than SVG.