FIX: Add word boundaries to replace and tag watched words (#13405)

The generated regular expressions did not contain \b which matched
every text that contained the word, even if it was only a substring of
a word.

For example, if "art" was a watched word a post containing word
"artist" matched.

app/assets/javascripts/discourse/tests/acceptance/admin-watched-words-test.js

@@ -118,7 +118,6 @@ acceptance("Admin - Watched Words - Bad regular expressions", function (needs) {
             action: "block",
           },
         ],
-        regular_expressions: true,
         compiled_regular_expressions: {
           block: null,
           censor: null,

app/assets/javascripts/discourse/tests/fixtures/watched-words-fixtures.js

@@ -11,14 +11,14 @@ export default {
       {
         id: 7,
         word: "hi",
-        regexp: "hi",
+        regexp: "(hi)",
         replacement: "hello",
         action: "replace",
       },
       {
         id: 8,
         word: "hello",
-        regexp: "hello",
+        regexp: "(hello)",
         replacement: "greeting",
         action: "tag",
       },

app/assets/javascripts/discourse/tests/unit/lib/pretty-text-test.js

@@ -1675,21 +1675,21 @@ var bar = 'bar';
 
   test("watched words replace", function (assert) {
     const opts = {
-      watchedWordsReplace: { fun: "times" },
+      watchedWordsReplace: { "(?:\\W|^)(fun)(?=\\W|$)": "times" },
     };
 
-    assert.cookedOptions("test fun", opts, "<p>test times</p>");
+    assert.cookedOptions("test fun funny", opts, "<p>test times funny</p>");
   });
 
   test("watched words link", function (assert) {
     const opts = {
-      watchedWordsLink: { fun: "https://discourse.org" },
+      watchedWordsLink: { "(?:\\W|^)(fun)(?=\\W|$)": "https://discourse.org" },
     };
 
     assert.cookedOptions(
-      "test fun",
+      "test fun funny",
       opts,
-      '<p>test <a href="https://discourse.org">fun</a></p>'
+      '<p>test <a href="https://discourse.org">fun</a> funny</p>'
     );
   });
 
@@ -1697,7 +1697,7 @@ var bar = 'bar';
     const maxMatches = 100; // same limit as MD watched-words-replace plugin
     const opts = {
       siteSettings: { watched_words_regular_expressions: true },
-      watchedWordsReplace: { "\\bu?\\b": "you" },
+      watchedWordsReplace: { "(\\bu?\\b)": "you" },
     };
 
     assert.cookedOptions(

app/assets/javascripts/pretty-text/engines/discourse-markdown/watched-words.js

@@ -20,8 +20,8 @@ function findAllMatches(text, matchers) {
       count++ < MAX_MATCHES
     ) {
       matches.push({
-        index: match.index,
-        text: match[0],
+        index: match.index + match[0].indexOf(match[1]),
+        text: match[1],
         replacement: matcher.replacement,
         link: matcher.link,
       });