Tilde \textasciitilde and fix ~ in \verb (#1286)

* \textasciitilde and fix ~ in \verb

* Add support for `\textasciitilde` which reproduces tilde character
  in text mode.
* Make `~` render as tilde instead of space within `\verb`,
  by manually mapping that character to `\textasciitilde`.
  This seems to be the only character that needs such manual mapping
  to reproduce LaTeX's `\verb` behavior.

* Add `, -, ', ~ to Verb screenshot test

src/functions/verb.js

@@ -25,7 +25,11 @@ defineFunction({
         // \verb enters text mode and therefore is sized like \textstyle
         const newOptions = options.havingStyle(options.style.text());
         for (let i = 0; i < text.length; i++) {
-            body.push(buildCommon.makeSymbol(text[i], "Typewriter-Regular",
+            let c = text[i];
+            if (c === '~') {
+                c = '\\textasciitilde';
+            }
+            body.push(buildCommon.makeSymbol(c, "Typewriter-Regular",
                 group.mode, newOptions, ["mord", "texttt"]));
         }
         buildCommon.tryCombineChars(body);

src/symbols.js

@@ -632,6 +632,7 @@ defineSymbol(text, main, textord, "|", "\\textbar"); // in T1 fontenc
 defineSymbol(math, main, textord, "\u2225", "\\|");
 defineSymbol(math, main, textord, "\u2225", "\\Vert");
 defineSymbol(text, main, textord, "\u2225", "\\textbardbl");
+defineSymbol(text, main, textord, "~", "\\textasciitilde");
 defineSymbol(math, main, rel, "\u2191", "\\uparrow", true);
 defineSymbol(math, main, rel, "\u21d1", "\\Uparrow", true);
 defineSymbol(math, main, rel, "\u2193", "\\downarrow", true);