Fix ligatures vs. \tt (#1379)

* Fix ligatures not always triggering

Example: \text{\rm --} would not cause ligature but should

* Remove ligatures in \texttt mode

* Add screenshot tests

* Fix MathML ligatures

* Fix type

* Handle \text... fonts in MathML building

* Remove leftover console deubgging

test/screenshotter/ss_data.yaml

@@ -76,7 +76,12 @@ Colors:
 ColorImplicit: bl{ack\color{red}red\textcolor{green}{green}red\color{blue}blue}black
 ColorSpacing: \textcolor{red}{\displaystyle \int x} + 1
 Colorbox:  a \colorbox{teal} B \fcolorbox{blue}{red}{C} e+\colorbox{teal}x
-DashesAndQuotes: \text{``a'' b---c -- d----`e'-{-}-f}--``x''
+DashesAndQuotes: |
+    \begin{array}{l}
+        \text{``a'' b---c -- d----`e'-{-}-f} -- \\
+        \text{\it ``a'' b---c -- d----`e'-{-}-f} ``x'' \\
+        \text{\tt ``a''---} \texttt{``a''---} \mathtt{--} \\
+    \end{array}
 DeepFontSizing:
     tex: |
         a^{\big| x^{\big(}}_{\Big\uparrow} +