Use weighted algorithm for string matching when finding files in repo (#21370)

This PR is for:
* https://github.com/go-gitea/gitea/issues/20231

Now, when a user searches `word`, they always see `/{word}.txt` before
`/{w}e-g{o}t-{r}esult.{d}at`

Demo:

When searching "a", "a.ext" comes first. 

Then when searching "at", the longer matched "template" comes first.

<details>


![image](https://user-images.githubusercontent.com/2114189/194588738-3644d891-956f-40e4-b79b-b97d34265456.png)


![image](https://user-images.githubusercontent.com/2114189/194588797-9b124670-4e1e-4510-a170-780295ed89b8.png)

</details>

This PR also makes the frontend tests could import feature JS files by
introducing `jestSetup.js`

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: silverwind <me@silverwind.io>

web_src/js/features/repo-findfile.test.js

@@ -0,0 +1,34 @@
+import {strSubMatch, calcMatchedWeight, filterRepoFilesWeighted} from './repo-findfile.js';
+
+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']);
+  });
+});