feat: \operatornamewithlimits (and clean up \operatorname support) (#2984)

* feat: \operatornamewithlimits (and clean up \operatorname support)

Add support for `\operatornamewithlimits` (an alias to `\operatorname*`
defined in `amsmath/amsopn.sty`), and use KaTeX's existing `\@ifstar`
macro to define `\operatorname` instead of a special lexing rule
(simplifying the lexer).

* Pick up one comment

* Actually fix docs this time

Co-authored-by: Ron Kok <ronkok@comcast.net>

src/Lexer.js

@@ -59,7 +59,6 @@ const tokenRegexString = `(${spaceRegexString}+)|` +  // whitespace
     `${combiningDiacriticalMarkString}*` +            // ...plus accents
     "|\\\\verb\\*([^]).*?\\4" +                       // \verb*
     "|\\\\verb([^*a-zA-Z]).*?\\5" +                   // \verb unstarred
-    "|\\\\operatorname\\*" +                          // \operatorname*
     `|${controlWordWhitespaceRegexString}` +          // \macroName + spaces
     `|${controlSymbolRegexString})`;                  // \\, \', etc.
 

src/functions/operatorname.js

@@ -1,5 +1,6 @@
 // @flow
 import defineFunction, {ordargument} from "../defineFunction";
+import {defineMacro} from "../macros";
 import buildCommon from "../buildCommon";
 import mathMLTree from "../mathMLTree";
 import {SymbolNode} from "../domTree";
@@ -140,7 +141,7 @@ const mathmlBuilder: MathMLBuilder<"operatorname"> = (group, options) => {
 // amsopn.dtx: \mathop{#1\kern\z@\operator@font#3}\newmcodes@
 defineFunction({
     type: "operatorname",
-    names: ["\\operatorname", "\\operatorname*"],
+    names: ["\\operatorname@", "\\operatornamewithlimits"],
     props: {
         numArgs: 1,
     },
@@ -150,7 +151,7 @@ defineFunction({
             type: "operatorname",
             mode: parser.mode,
             body: ordargument(body),
-            alwaysHandleSupSub: (funcName === "\\operatorname*"),
+            alwaysHandleSupSub: (funcName === "\\operatornamewithlimits"),
             limits: false,
             parentIsSupSub: false,
         };
@@ -159,3 +160,5 @@ defineFunction({
     mathmlBuilder,
 });
 
+defineMacro("\\operatorname",
+  "\\@ifstar\\operatornamewithlimits\\operatorname@");