Add category theory LaTeX symbols (turnstiles, corners, arrows)

[rzil]

Adds several commonly-used category theory and logic LaTeX symbols that
are already present in the bundled math fonts but were not exposed via
supportedLatexSymbols.

Includes:

• Turnstiles: \vdash, \dashv, \vDash, \Vdash, \Dashv
• Pullback / pushout markers: \ulcorner, \urcorner, \llcorner, \lrcorner
• Diagram arrows: \hookrightarrow, \twoheadrightarrow, \rightarrowtail,
  \leftrightarrows, \rightleftarrows

Example:

\begin{pmatrix}
P & \to & B \\
\downarrow & \ulcorner & \downarrow \\
A & \to & C
\end{pmatrix}

All changes are additive and limited to MTMathAtomFactory.

[mgriebling]

Sorry there are conflicts with this merge request. Can you please fix these?