Fix WorkspaceRoot encoding preference lookup and persistence

[deepika-u]

Fixes two issues in how WorkspaceRoot reads and writes the workspace default encoding preference.

1. getDefaultCharset() - now reads the encoding via Platform.getPreferencesService() instead of the instance-scope node
   directly, so it correctly falls back through the scope search order instead of only checking one scope.

2. setDefaultCharset() - removed the custom override. Since WorkspaceRoot's path is always IPath.ROOT, it now inherits
   Container#setDefaultCharset(String), which already delegates to CharsetManager and reports save failures as a CoreException instead of silently logging them.

Partially fixes
#497

[deepika-u]

@HeikoKlare - When you get some time, can you take a look at this please?

[Copilot]

🟡 Changes recommended

Preference lookup and persistence error handling must preserve existing behavior and API contracts.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Modernizes WorkspaceRoot by replacing legacy preferences with IEclipsePreferences.

Changes:

• Uses scoped preferences for workspace encoding.
• Explicitly flushes updates and logs persistence failures.

File summaries

File	Review
resources/bundles/org.eclipse.core.resources/src/org/eclipse/core/internal/resources/WorkspaceRoot.java	Two moderate issues (2 votes each): default-scope encoding values are no longer resolved, and flush failures are logged instead of reported as CoreException per the API contract.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 2
• Review effort level: Balanced

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[github-actions]

Test Results

    54 files  ±0      54 suites  ±0   58m 4s ⏱️ - 1m 30s
 4 810 tests ±0   4 786 ✅  - 2   22 💤 ±0  1 ❌ +1  1 🔥 +1 
12 321 runs  ±0  12 166 ✅  - 2  153 💤 ±0  1 ❌ +1  1 🔥 +1 

For more details on these failures and errors, see this check.

Results for commit 2eef6c6. ± Comparison against base commit 2d15cf3.

♻️ This comment has been updated with latest results.

[Copilot]

🟢 Approval recommended

The reviewed change has no unresolved approval-blocking issues.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[deepika-u]

Do you think any other actions are still pending? If not, can this be approved and merged now?

[deepika-u]

@iloveeclipse : Do you want me to check anything else on this pr? or can this be merged?