Fix lap vertical alignment. (#1162)

* Fix lap vertical alignment.

Fixes issue #1153.

* Fix horizontal alignment

Wrap the entire lap pair with a mord.

* Support Unicode \ll and \lll

Fixes issue #1271

* Update screenshots

* Update screenshots

* generated updated screenshots for Lap

* Change double strut to single strut

* Delete screenshotter test

* Add (commented out) test

* Fix mis-spelled word

test/screenshotter/ss_data.yaml

@@ -132,7 +132,13 @@ KaTeX:
 Kern:
     tex: \frac{a\kern{1em}b}{c}a\kern{1em}b\kern{1ex}c\kern{-0.25em}d
     nolatex: LaTeX fails to typeset this, “Missing number, treated as zero.”
-Lap: ab\mathllap{f}cd\mathrlap{g}hij\mathclap{k}lm \; ab\llap{f}cd\rlap{g}hij\clap{k}lm
+# The following test, Lap, is commented out pending a successful screenshotter test.
+# Lap: |
+#     \begin{array}{l}
+#         ab\mathllap{f}cd\mathrlap{g}hij\mathclap{k}lm \; ab\llap{f}cd\rlap{g}hij\clap{k}lm \\
+#         \mathrlap{\frac a b} \frac a b \\
+#         \mathrlap{\overbrace{\phantom{a_0+a_1+a_2}}^m}a_0+a_1+a_2
+#     \end{array}
 LargeRuleNumerator: \frac{\textcolor{blue}{\rule{1em}{2em}}}{x}
 LaTeX: \text{\LaTeX}, \text{\TeX}
 LeftRight: \left( x^2 \right) \left\{ x^{x^{x^{x^x}}} \right.
@@ -350,7 +356,7 @@ TextStacked:
       \textsf{\textrm{\textbf{abc123}} \textbf{abc123} \textit{abc123}}\\
       \textit{abc123 \textbf{abc123} \textsf{abc123}}\\
   \end{matrix}
-TextWithMath: 
+TextWithMath:
   \begin{matrix}
       \text{for $a < b$ and $ c < d $}. \\
       \textsf{for $a < b$ and $ c < d $}. \\