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/components/DiffCommitSelector.vue

@@ -1,5 +1,6 @@
 <script>
 import {SvgIcon} from '../svg.js';
+import {GET} from '../modules/fetch.js';
 
 export default {
   components: {SvgIcon},
@@ -123,7 +124,7 @@ export default {
     },
     /** Load the commits to show in this dropdown */
     async fetchCommits() {
-      const resp = await fetch(`${this.issueLink}/commits/list`);
+      const resp = await GET(`${this.issueLink}/commits/list`);
       const results = await resp.json();
       this.commits.push(...results.commits.map((x) => {
         x.hovered = false;