feat: Support matrix*, pmatrix*, bmatrix*, Bmatrix*, vmatrix*, and Vmatrix*. (#2488)

* Support matrix*, pmatrix*, bmatrix*, Bmatrix*, vmatrix*, and Vmatrix*

* Add tests and docs

* Delete screeshotter tests

* Fix column alignment and add bogus screenshot files

* Update real Chrome and Firefox screenshots.

* Update Safari screenshot

* Dedupe code in array.js

* Edit payload in array.js

* Edit again, correctly this time.

test/__snapshots__/katex-spec.js.snap

@@ -115,6 +115,16 @@ exports[`A begin/end parser should grab \\arraystretch 1`] = `
         }
       ]
     ],
+    "cols": [
+      {
+        "type": "align",
+        "align": "c"
+      },
+      {
+        "type": "align",
+        "align": "c"
+      }
+    ],
     "hLinesBeforeRow": [
       [
       ],

test/katex-spec.js

@@ -1300,6 +1300,17 @@ describe("A begin/end parser", function() {
         const parse = getParsed`\def\arraystretch{1.5}\begin{matrix}a&b\\c&d\end{matrix}`;
         expect(parse).toMatchSnapshot();
     });
+
+    it("should allow an optional argument in {matrix*} and company.", function() {
+        expect("\\begin{matrix*}[r] a & -1 \\\\ -1 & d \\end{matrix*}").toBuild();
+        expect("\\begin{pmatrix*}[r] a & -1 \\\\ -1 & d \\end{pmatrix*}").toBuild();
+        expect("\\begin{bmatrix*}[r] a & -1 \\\\ -1 & d \\end{bmatrix*}").toBuild();
+        expect("\\begin{Bmatrix*}[r] a & -1 \\\\ -1 & d \\end{Bmatrix*}").toBuild();
+        expect("\\begin{vmatrix*}[r] a & -1 \\\\ -1 & d \\end{vmatrix*}").toBuild();
+        expect("\\begin{Vmatrix*}[r] a & -1 \\\\ -1 & d \\end{Vmatrix*}").toBuild();
+        expect("\\begin{matrix*} a & -1 \\\\ -1 & d \\end{matrix*}").toBuild();
+        expect("\\begin{matrix*}[] a & -1 \\\\ -1 & d \\end{matrix*}").not.toParse();
+    });
 });
 
 describe("A sqrt parser", function() {

test/screenshotter/ss_data.yaml

@@ -244,6 +244,7 @@ MathOp: a\mathop+b\mathop:c\mathop{\delta}e\mathop{\textrm{and}}f\mathrel{\matho
 MathRm: \mathrm{Ax2k\breve{a}\omega\Omega\imath+\KaTeX}
 MathSf: \mathsf{Ax2k\breve{a}\omega\Omega\imath+\KaTeX}
 MathScr: \mathscr{Ax2k\breve{a}\omega\Omega\imath+\KaTeX}
+MathtoolsMatrix: \begin{matrix*}[l] a & -1 \\ -1 & d \end{matrix*} \; \begin{pmatrix*}[r] a & -1 \\ -1 & d \end{pmatrix*}
 MathTt: \mathtt{Ax2k\breve{a}\omega\Omega\imath+\KaTeX}
 Mod: |
     \begin{array}{cc}