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

[charlescordialDevExpress]

What does the PR change?

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

How did you achieve this?

1. Reviewed the scheduler-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 scheduler-related widget demos.
3. Confirm that the demos render correctly without import or module resolution errors.
4. Verify that all scheduler-related widgets function as expected

[Copilot]

Pull request overview

This PR updates Scheduler-related demo apps (Vue/React/Angular) to ensure DevExtreme widgets referenced by string (widget="dxButton", editorType="dxSelectBox") are properly registered via explicit side-effect imports, aligning the demos with modular import behavior.

Changes:

• Added import 'devextreme/ui/button' to Scheduler Toolbar demos where toolbar items instantiate dxButton by widget name.
• Added import 'devextreme/ui/select_box' to Scheduler Templates demos where form items instantiate dxSelectBox by editorType.
• Removed DxButtonModule from the Angular Scheduler Toolbar demo’s standalone imports list since the demo doesn’t render an Angular <dx-button> component.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
apps/demos/Demos/Scheduler/Toolbar/Vue/App.vue	Registers dxButton for Scheduler toolbar items using widget="dxButton".
apps/demos/Demos/Scheduler/Toolbar/ReactJs/App.js	Registers dxButton for Scheduler toolbar items using widget="dxButton".
apps/demos/Demos/Scheduler/Toolbar/React/App.tsx	Registers dxButton for Scheduler toolbar items using widget="dxButton".
apps/demos/Demos/Scheduler/Toolbar/Angular/app/app.component.ts	Registers dxButton via side-effect import and removes unused DxButtonModule from standalone imports.
apps/demos/Demos/Scheduler/Templates/Vue/App.vue	Registers dxSelectBox for Scheduler form items using editor-type="dxSelectBox".
apps/demos/Demos/Scheduler/Templates/ReactJs/App.js	Registers dxSelectBox for Scheduler form items using editorType="dxSelectBox".
apps/demos/Demos/Scheduler/Templates/React/App.tsx	Registers dxSelectBox for Scheduler form items using editorType="dxSelectBox".
apps/demos/Demos/Scheduler/Templates/Angular/app/app.component.ts	Registers dxSelectBox for Scheduler form items using editorType="dxSelectBox".