Use fetch helpers instead of fetch (#27026)

WIP because:

- [x] Some calls set a `content-type` but send no body, can likely
remove the header
- [x] Need to check whether `charset=utf-8` has any significance on the
webauthn calls, I assume not as it is the default for json content.
- [x] Maybe `no-restricted-globals` is better for eslint, but will
require a lot of duplication in the yaml or moving eslint config to a
`.js` extension.
- [x] Maybe export `request` as `fetch`, shadowing the global.

web_src/js/features/repo-diff-commit.js

@@ -1,9 +1,10 @@
 import {hideElem, showElem, toggleElem} from '../utils/dom.js';
+import {GET} from '../modules/fetch.js';
 
 async function loadBranchesAndTags(area, loadingButton) {
   loadingButton.classList.add('disabled');
   try {
-    const res = await fetch(loadingButton.getAttribute('data-fetch-url'));
+    const res = await GET(loadingButton.getAttribute('data-fetch-url'));
     const data = await res.json();
     hideElem(loadingButton);
     addTags(area, data.tags);