Scheduler - Appointment Form - Reimplement legacy QUnit tests for the new form - Part 2

[Tucchhaa]

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[Copilot]

Pull request overview

This PR continues the reimplementation of legacy QUnit tests for the Scheduler appointment form as Jest tests (Part 2). It adds additional test coverage for editing recurring appointments, resource field expressions, resource editor types, and resource dataSource loading behavior.

Key Changes:

• Added 4 new tests covering recurring appointment editing, resource field handling, and resource editor types
• Added getEditAppointmentButton() helper method to PopupModel for accessing the "Edit appointment" button
• Renamed test suite from "Timezones" to "Timezone Editors" for better clarity

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
packages/devextreme/js/__internal/scheduler/appointment_popup/appointment_popup.test.ts	Added 4 new tests: single appointment from series editing, resource field expression validation, resource editor type verification (TagBox vs SelectBox), and resource dataSource loading optimization test
packages/devextreme/js/__internal/scheduler/tests/mock/model/popup.ts	Added getEditAppointmentButton() helper method following the same pattern as getEditSeriesButton()