fix: decode only percent-encoded escapes in decodeURIComponent (#25672) (CP: 25.2)

[Artur-]

UrlUtil.decodeURIComponent treated every non-ASCII character as a raw UTF-8 byte, even when it was never percent-encoded, so paths that already contain literal characters like ü or 日 were corrupted into the replacement character. Now only real %XX escapes are decoded and all other characters are left untouched.

Backport of #25672 to 25.2. The ResourceFolderUtilTest case from the original PR is omitted because ResourceFolderUtil does not exist on 25.2.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Test Results

 1 385 files  ±0   1 385 suites  ±0   1h 32m 42s ⏱️ + 1m 53s
10 427 tests +4  10 359 ✅ +4  68 💤 ±0  0 ❌ ±0 
10 782 runs  +4  10 713 ✅ +4  69 💤 ±0  0 ❌ ±0 

Results for commit 507b020. ± Comparison against base commit b948369.

[vaadin-bot]

Hi @Artur- and @Artur-, when i performed cherry-pick to this commit to 24.10, i have encountered the following issue. Can you take a look and pick it manually?
Error Message:
Error: Command failed: git cherry-pick ad7c003
error: could not apply ad7c003... fix: decode only percent-encoded escapes in decodeURIComponent (#25672) (CP: 25.2) (#25735)
hint: After resolving the conflicts, mark them with
hint: "git add/rm ", then run
hint: "git cherry-pick --continue".
hint: You can instead skip this commit with "git cherry-pick --skip".
hint: To abort and get back to the state before "git cherry-pick",
hint: run "git cherry-pick --abort".

[vaadin-bot]

This ticket/PR has been released with Vaadin 25.2.9.