Convert frontend code to typescript (#31559)

None of the frontend js/ts files was touched besides these two commands
(edit: no longer true, I touched one file in
61105d0618
because of a deprecation that was not showing before the rename).

`tsc` currently reports 778 errors, so I have disabled it in CI as
planned.

Everything appears to work fine.

web_src/js/features/pull-view-file.ts

@@ -0,0 +1,96 @@
+import {diffTreeStore} from '../modules/stores.ts';
+import {setFileFolding} from './file-fold.ts';
+import {POST} from '../modules/fetch.ts';
+
+const {pageData} = window.config;
+const prReview = pageData.prReview || {};
+const viewedStyleClass = 'viewed-file-checked-form';
+const viewedCheckboxSelector = '.viewed-file-form'; // Selector under which all "Viewed" checkbox forms can be found
+const expandFilesBtnSelector = '#expand-files-btn';
+const collapseFilesBtnSelector = '#collapse-files-btn';
+
+// Refreshes the summary of viewed files if present
+// The data used will be window.config.pageData.prReview.numberOf{Viewed}Files
+function refreshViewedFilesSummary() {
+  const viewedFilesProgress = document.querySelector('#viewed-files-summary');
+  viewedFilesProgress?.setAttribute('value', prReview.numberOfViewedFiles);
+  const summaryLabel = document.querySelector('#viewed-files-summary-label');
+  if (summaryLabel) summaryLabel.innerHTML = summaryLabel.getAttribute('data-text-changed-template')
+    .replace('%[1]d', prReview.numberOfViewedFiles)
+    .replace('%[2]d', prReview.numberOfFiles);
+}
+
+// Explicitly recounts how many files the user has currently reviewed by counting the number of checked "viewed" checkboxes
+// Additionally, the viewed files summary will be updated if it exists
+export function countAndUpdateViewedFiles() {
+  // The number of files is constant, but the number of viewed files can change because files can be loaded dynamically
+  prReview.numberOfViewedFiles = document.querySelectorAll(`${viewedCheckboxSelector} > input[type=checkbox][checked]`).length;
+  refreshViewedFilesSummary();
+}
+
+// Initializes a listener for all children of the given html element
+// (for example 'document' in the most basic case)
+// to watch for changes of viewed-file checkboxes
+export function initViewedCheckboxListenerFor() {
+  for (const form of document.querySelectorAll(`${viewedCheckboxSelector}:not([data-has-viewed-checkbox-listener="true"])`)) {
+    // To prevent double addition of listeners
+    form.setAttribute('data-has-viewed-checkbox-listener', true);
+
+    // The checkbox consists of a div containing the real checkbox with its label and the CSRF token,
+    // hence the actual checkbox first has to be found
+    const checkbox = form.querySelector('input[type=checkbox]');
+    checkbox.addEventListener('input', function() {
+      // Mark the file as viewed visually - will especially change the background
+      if (this.checked) {
+        form.classList.add(viewedStyleClass);
+        checkbox.setAttribute('checked', '');
+        prReview.numberOfViewedFiles++;
+      } else {
+        form.classList.remove(viewedStyleClass);
+        checkbox.removeAttribute('checked');
+        prReview.numberOfViewedFiles--;
+      }
+
+      // Update viewed-files summary and remove "has changed" label if present
+      refreshViewedFilesSummary();
+      const hasChangedLabel = form.parentNode.querySelector('.changed-since-last-review');
+      hasChangedLabel?.remove();
+
+      const fileName = checkbox.getAttribute('name');
+
+      // check if the file is in our difftreestore and if we find it -> change the IsViewed status
+      const fileInPageData = diffTreeStore().files.find((x) => x.Name === fileName);
+      if (fileInPageData) {
+        fileInPageData.IsViewed = this.checked;
+      }
+
+      // Unfortunately, actual forms cause too many problems, hence another approach is needed
+      const files = {};
+      files[fileName] = this.checked;
+      const data = {files};
+      const headCommitSHA = form.getAttribute('data-headcommit');
+      if (headCommitSHA) data.headCommitSHA = headCommitSHA;
+      POST(form.getAttribute('data-link'), {data});
+
+      // Fold the file accordingly
+      const parentBox = form.closest('.diff-file-header');
+      setFileFolding(parentBox.closest('.file-content'), parentBox.querySelector('.fold-file'), this.checked);
+    });
+  }
+}
+
+export function initExpandAndCollapseFilesButton() {
+  // expand btn
+  document.querySelector(expandFilesBtnSelector)?.addEventListener('click', () => {
+    for (const box of document.querySelectorAll('.file-content[data-folded="true"]')) {
+      setFileFolding(box, box.querySelector('.fold-file'), false);
+    }
+  });
+  // collapse btn, need to exclude the div of “show more”
+  document.querySelector(collapseFilesBtnSelector)?.addEventListener('click', () => {
+    for (const box of document.querySelectorAll('.file-content:not([data-folded="true"])')) {
+      if (box.getAttribute('id') === 'diff-incomplete') continue;
+      setFileFolding(box, box.querySelector('.fold-file'), true);
+    }
+  });
+}