fix(auto-render): strict dollar delimiter

The dollar delimiter, especially the non-display version, is disabled by default
because it often causes errors in determining the boundary when there are at
least two numbers followed by the `$` symbol present in one paragraph.

This change makes it possible to make the delimiter stricter in determining
the math boundary, by checking what characters come before the opening delimiter
and what characters come after the closing delimiter.

Tests are available as follows:

~~~ html
<ul>
  <li>$E=mc^2$</li>
  <li>$E=mc^2$asdf</li>
  <li>asdf$E=mc^2$</li>
  <li>asdf$E=mc^2$asdf</li>
  <li>$E=mc^2$ asdf</li>
  <li>asdf $E=mc^2$</li>
  <li>asdf $E=mc^2$ asdf</li>
  <li>($E=mc^2$)asdf</li>
  <li>asdf($E=mc^2$)</li>
  <li>asdf($E=mc^2$)asdf</li>
  <li>asdf asdf 20$ asdf 30$ asdf asdf asdf</li>
  <li>asdf asdf $20 asdf $30 asdf asdf asdf</li>
  <li>asdf asdf $20 asdf 30$ asdf asdf asdf</li>
  <li>asdf asdf 20 $ asdf 30 $ asdf asdf asdf</li>
  <li>asdf asdf $ 20 asdf $ 30 asdf asdf asdf</li>
  <li>asdf asdf $ 20 asdf 30 $ asdf asdf asdf</li>
</ul>

<ul>
  <li>$$E=mc^2$$</li>
  <li>$$E=mc^2$$asdf</li>
  <li>asdf$$E=mc^2$$</li>
  <li>asdf$$E=mc^2$$asdf</li>
  <li>$$E=mc^2$$ asdf</li>
  <li>asdf $$E=mc^2$$</li>
  <li>asdf $$E=mc^2$$ asdf</li>
  <li>($$E=mc^2$$)asdf</li>
  <li>asdf($$E=mc^2$$)</li>
  <li>asdf($$E=mc^2$$)asdf</li>
  <li>asdf asdf 20$$ asdf 30$$ asdf asdf asdf</li>
  <li>asdf asdf $$20 asdf $$30 asdf asdf asdf</li>
  <li>asdf asdf $$20 asdf 30$$ asdf asdf asdf</li>
  <li>asdf asdf 20 $$ asdf 30 $$ asdf asdf asdf</li>
  <li>asdf asdf $$ 20 asdf $$ 30 asdf asdf asdf</li>
  <li>asdf asdf $$ 20 asdf 30 $$ asdf asdf asdf</li>
</ul>

<ul>
  <li>asdf +10$ asdf -10$ asdf</li>
  <li>asdf +10 $ asdf -10 $ asdf</li>
  <li>asdf $+10 asdf $-10 asdf</li>
  <li>asdf $ +10 asdf $ -10 asdf</li>
</ul>

<ul>
  <li>asdf +10.5$ asdf -10.5$ asdf</li>
  <li>asdf +10.5 $ asdf -10.5 $ asdf</li>
  <li>asdf $+10.5 asdf $-10.5 asdf</li>
  <li>asdf $ +10.5 asdf $ -10.5 asdf</li>
</ul>

<ul>
  <li>asdf +10,5$ asdf -10,5$ asdf</li>
  <li>asdf +10,5 $ asdf -10,5 $ asdf</li>
  <li>asdf $+10,5 asdf $-10,5 asdf</li>
  <li>asdf $ +10,5 asdf $ -10,5 asdf</li>
</ul>

<ul>
  <li>asdf +10,000,000.5$ asdf -10,000,000.5$ asdf</li>
  <li>asdf +10,000,000.5 $ asdf -10,000,000.5 $ asdf</li>
  <li>asdf $+10,000,000.5 asdf $-10,000,000.5 asdf</li>
  <li>asdf $ +10,000,000.5 asdf $ -10,000,000.5 asdf</li>
</ul>

<ul>
  <li>asdf +10.000.000,5$ asdf -10.000.000,5$ asdf</li>
  <li>asdf +10.000.000,5 $ asdf -10.000.000,5 $ asdf</li>
  <li>asdf $+10.000.000,5 asdf $-10.000.000,5 asdf</li>
  <li>asdf $ +10.000.000,5 asdf $ -10.000.000,5 asdf</li>
</ul>

<ul>
  <li>asdf1234$E=mc^2$</li>
  <li>asdf1234$E=mc^2$1234asdf</li>
  <li>$E=mc^2$1234asdf</li>
  <li>asdf1234 $E=mc^2$</li>
  <li>asdf1234 $E=mc^2$ 1234asdf</li>
  <li>$E=mc^2$ 1234asdf</li>
</ul>
~~~

contrib/auto-render/splitAtDelimiters.js

@@ -63,13 +63,26 @@ const splitAtDelimiters = function(text, delimiters) {
         const math = amsRegex.test(rawData)
             ? rawData
             : text.slice(delimiters[i].left.length, index);
-        data.push({
-            type: "math",
-            data: math,
-            rawData,
-            display: delimiters[i].display,
-        });
+        let previousData = data.slice(-1).pop(),
+            // Treat current data as plain text if previous data ends with any words or any numbers with optional space after them
+            currentData = previousData && /(\w|\b[+-]?\d+([,.]\d+)*\s*)$/.test(previousData.data) && rawData[0] === '$' ? {
+                type: "text",
+                data: rawData,
+            } : {
+                type: "math",
+                data: math,
+                rawData,
+                display: delimiters[i].display,
+            };
         text = text.slice(index + delimiters[i].right.length);
+        // Treat current data as plain text if next data starts with any words or any numbers with optional space after them
+        if (currentData.type === "math" && /^(\w|\s*[+-]?\d+([,.]\d+)*\b)/.test(text) && currentData.rawData[0] === '$') {
+            currentData.type = "text";
+            currentData.data = currentData.rawData;
+            delete currentData.display;
+            delete currentData.rawData;
+        }
+        data.push(currentData);
     }
 
     if (text !== "") {
@@ -82,4 +95,4 @@ const splitAtDelimiters = function(text, delimiters) {
     return data;
 };
 
-export default splitAtDelimiters;
+export default splitAtDelimiters;