Preference changes not registered when settings.json open in editor.

[colin-grant-work]

Bug Description:

This bug is a follow up to ongoing work on #7105. When a preference file is open in the editor, changes in the GUI are written to the file, but the file is not saved. In VSCode, if the file is not dirty when a preference change is made in the GUI, the file is automatically saved.

Steps to Reproduce:

1. Using the code from Added Preferences UI widget #7105,
2. Open the preferences GUI
3. Open the preferences file corresponding to your current scope (e.g. by clicking the {} in the upper right.)
4. Modify preferences in the GUI
5. Observe that the preferences changes are not registered by the GUI (no blue bars appear), that the file is marked as dirty, and that the preference changes are written to it, but not saved.

Additional Information

The current behavior is governed by a call to applyBackgroundEdit here:

theia/packages/preferences/src/browser/abstract-resource-preference-provider.ts

Line 154 in 9286ffe

await this.workspace.applyBackgroundEdit(this.model, editOperations);

That method explicitly does not save the file if the editor is open.

• Operating System: RHEL7
• Theia Version: Master (1.1.0)