feat: support {align}, {align*}, {alignat}, and {alignat*} (#2341)

* Support {align}, {align*}, {alignat}, and {alignat*}

* Specify display mode for screenshots

* Add bogus screenshots

* Some screenshotter progress

* Update screenshots

test/katex-spec.js

@@ -2726,25 +2726,26 @@ describe("An aligned environment", function() {
     });
 });
 
-describe("A gather environment", function() {
+describe("AMS environments", function() {
     const nonStrictDisplay = new Settings({displayMode: true, strict: false});
 
     it("should fail outside display mode", () => {
         expect`\begin{gather}a+b\\c+d\end{gather}`.not.toParse(nonstrictSettings);
-    });
-
-    it("should fail outside display mode", () => {
         expect`\begin{gather*}a+b\\c+d\end{gather*}`.not.toParse(nonstrictSettings);
+        expect`\begin{align}a&=b+c\\d+e&=f\end{align}`.not.toParse(nonstrictSettings);
+        expect`\begin{align*}a&=b+c\\d+e&=f\end{align*}`.not.toParse(nonstrictSettings);
+        expect`\begin{alignat}{2}10&x+ &3&y = 2\\3&x+&13&y = 4\end{alignat}`.not.toParse(nonstrictSettings);
+        expect`\begin{alignat*}{2}10&x+ &3&y = 2\\3&x+&13&y = 4\end{alignat*}`.not.toParse(nonstrictSettings);
     });
 
-    it("should build if in display mode", () => {
+    it("should build if in non-strict display mode", () => {
         expect`\begin{gather}a+b\\c+d\end{gather}`.toBuild(nonStrictDisplay);
-    });
-
-    it("should build if in display mode", () => {
         expect`\begin{gather*}a+b\\c+d\end{gather*}`.toBuild(nonStrictDisplay);
+        expect`\begin{align}a&=b+c\\d+e&=f\end{align}`.toBuild(nonStrictDisplay);
+        expect`\begin{align*}a&=b+c\\d+e&=f\end{align*}`.toBuild(nonStrictDisplay);
+        expect`\begin{alignat}{2}10&x+ &3&y = 2\\3&x+&13&y = 4\end{alignat}`.toBuild(nonStrictDisplay);
+        expect`\begin{alignat*}{2}10&x+ &3&y = 2\\3&x+&13&y = 4\end{alignat*}`.toBuild(nonStrictDisplay);
     });
-
 });
 
 describe("operatorname support", function() {

test/screenshotter/ss_data.yaml

@@ -22,6 +22,9 @@ AccentsText: |
     \text{\'A} & \text{\.A} & \text{\`A} & \text{\"A} & \text{\H{A}} & \text{\r{A}} \\
     \text{\.I İ} & \text{\H e e̋} & \text{\i ı}
     \end{array}
+Align:
+    tex: \begin{align}a &= 1 & b &= 2 \\ 3a &= 3 & 17b &= 34\end{align}
+    display: 1
 Aligned: |
     \begin{aligned}
         a &= 1 & b &= 2 \\