feat: Add partial quoting

- If you select a portion of the comment, `Quote reply` will not only
quote that portion and not copy paste the whole text as it previously
did. This is achieved by using the `@github/quote-selection` package.
- There's preprocessing to ensure Forgejo-flavored markdown syntax is
preserved.
- e2e test added.
- Resolves #1342

tests/e2e/e2e_test.go

@@ -49,7 +49,9 @@ func TestMain(m *testing.M) {
 
 	err := unittest.InitFixtures(
 		unittest.FixturesOptions{
-			Dir: filepath.Join(filepath.Dir(setting.AppPath), "models/fixtures/"),
+			Dir:  filepath.Join(setting.AppWorkPath, "models/fixtures/"),
+			Base: setting.AppWorkPath,
+			Dirs: []string{"tests/e2e/fixtures/"},
 		},
 	)
 	if err != nil {