fix: stablize jrejsmap in flow-client

[lycoris106]

Description

Part of #22767

This PR together with some previous ones should resolve all the flaky tests currently found in the flow repo. Here the non-deterministic test is JreMapTest.testMapValues in flow-client.

Root Cause

The non-deterministic is from for (Entry<K, V> entry : values.entrySet()) iteration in JRE Map's forEach method. The assertion in the test assumes it preserves the insertion order.

Fix

Switched HashMap to LinkedHashMap so iteration order preserves insertion order just like JavaScript Map. We can choose to relax the assertion instead, but considering this is a fallback for JavaScript Map, we try to follow its behavior.

Note

This is the last PR for the issue #22767. If this is accepted I will close the issue.

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.

Additional for Feature type of change

• Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.

[github-actions]

Test Results

1 300 files  ± 0  1 300 suites  ±0   1h 15m 51s ⏱️ +54s
9 102 tests ± 0  9 034 ✅ ± 0  68 💤 ±0  0 ❌ ±0 
9 539 runs   - 19  9 463 ✅  - 19  76 💤 ±0  0 ❌ ±0 

Results for commit 5ff16aa. ± Comparison against base commit 1af987a.