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/repo-findfile.test.ts

@@ -0,0 +1,34 @@
+import {strSubMatch, calcMatchedWeight, filterRepoFilesWeighted} from './repo-findfile.ts';
+
+describe('Repo Find Files', () => {
+  test('strSubMatch', () => {
+    expect(strSubMatch('abc', '')).toEqual(['abc']);
+    expect(strSubMatch('abc', 'a')).toEqual(['', 'a', 'bc']);
+    expect(strSubMatch('abc', 'b')).toEqual(['a', 'b', 'c']);
+    expect(strSubMatch('abc', 'c')).toEqual(['ab', 'c']);
+    expect(strSubMatch('abc', 'ac')).toEqual(['', 'a', 'b', 'c']);
+    expect(strSubMatch('abc', 'z')).toEqual(['abc']);
+    expect(strSubMatch('abc', 'az')).toEqual(['abc']);
+
+    expect(strSubMatch('ABc', 'ac')).toEqual(['', 'A', 'B', 'c']);
+    expect(strSubMatch('abC', 'ac')).toEqual(['', 'a', 'b', 'C']);
+
+    expect(strSubMatch('aabbcc', 'abc')).toEqual(['', 'a', 'a', 'b', 'b', 'c', 'c']);
+    expect(strSubMatch('the/directory', 'hedir')).toEqual(['t', 'he', '/', 'dir', 'ectory']);
+  });
+
+  test('calcMatchedWeight', () => {
+    expect(calcMatchedWeight(['a', 'b', 'c', 'd']) < calcMatchedWeight(['a', 'bc', 'c'])).toBeTruthy();
+  });
+
+  test('filterRepoFilesWeighted', () => {
+    // the first matched result should always be the "word.txt"
+    let res = filterRepoFilesWeighted(['word.txt', 'we-got-result.dat'], 'word');
+    expect(res).toHaveLength(2);
+    expect(res[0].matchResult).toEqual(['', 'word', '.txt']);
+
+    res = filterRepoFilesWeighted(['we-got-result.dat', 'word.txt'], 'word');
+    expect(res).toHaveLength(2);
+    expect(res[0].matchResult).toEqual(['', 'word', '.txt']);
+  });
+});