tools: replace for loop with map()

Refs: #41406 (comment)
Co-authored-by: Tobias Nießen <tniessen@tnie.de>

PR-URL: #41451
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>

tools/doc/allhtml.mjs

@@ -101,12 +101,8 @@ all = all.slice(0, apiStart.index + apiStart[0].length) +
 fs.writeFileSync(new URL('./all.html', source), all, 'utf8');
 
 // Validate all hrefs have a target.
-const ids = new Set();
 const idRe = / id="([^"]+)"/g;
-const idMatches = all.matchAll(idRe);
-for (const match of idMatches) {
-  ids.add(match[1]);
-}
+const ids = new Set([...all.matchAll(idRe)].map((match) => match[1]));
 
 const hrefRe = / href="#([^"]+)"/g;
 const hrefMatches = all.matchAll(hrefRe);