WG Demos - Update editorType/widget import statements for editor-related widget demos

[charlescordialDevExpress]

What does the PR change?

1. Updates the editorType and widget import statements in editor-related widget demos to use the correct module references.

How did you achieve this?

1. Reviewed the editor-related widget demos that use editorType and widget imports.
2. Updated the import statements to align with the current module structure and import conventions.
3. Verified that the affected demos compile and load successfully after the changes.

How can we verify these changes?

1. Build and run the WG Demos project.
2. Open the editor-related widget demos.
3. Confirm that the demos render correctly without import or module resolution errors.
4. Verify that all editor widgets function as expected

[Copilot]

Pull request overview

Updates WG demo sources to ensure DevExtreme editor-related toolbar items that render dxButton via widget="dxButton" have the required modular widget registration import.

Changes:

• Added side-effect imports for devextreme/ui/button in Vue/React popup and HtmlEditor toolbar customization demos so dxButton is registered when referenced via widget="dxButton".
• Updated the Angular HtmlEditor toolbar customization demo with a side-effect import (but currently for the wrong widget module).

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
apps/demos/Demos/Popup/Overview/Vue/App.vue	Adds devextreme/ui/button import to support DxToolbarItem widget="dxButton".
apps/demos/Demos/Popup/Overview/ReactJs/App.js	Adds devextreme/ui/button import to support ToolbarItem widget="dxButton".
apps/demos/Demos/Popup/Overview/React/App.tsx	Adds devextreme/ui/button import to support ToolbarItem widget="dxButton" (typed options).
apps/demos/Demos/HtmlEditor/ToolbarCustomization/Vue/App.vue	Adds devextreme/ui/button import to support toolbar item widget="dxButton".
apps/demos/Demos/HtmlEditor/ToolbarCustomization/ReactJs/App.js	Adds devextreme/ui/button import to support toolbar item widget="dxButton".
apps/demos/Demos/HtmlEditor/ToolbarCustomization/React/App.tsx	Adds devextreme/ui/button import to support toolbar item widget="dxButton".
apps/demos/Demos/HtmlEditor/ToolbarCustomization/Angular/app/app.component.ts	Adds a side-effect import, but it currently imports button_group while the demo uses dxButton.