Overlay: Add zIndex option & specify it for LoadPanel in Grid (T1308742)

[r-farkhutdinov]

No description provided.

[Copilot]

Pull request overview

This PR adds a zIndex option to the Overlay widget and applies it to the LoadPanel in DataGrid/TreeGrid to fix z-index layering issues (T1308742). The implementation allows users to specify a custom z-index value instead of relying solely on the automatic z-index pool management.

Key Changes

• Added zIndex option to Overlay widget allowing custom z-index values
• Refactored z-index management logic to support both pool-based and custom z-index values
• Set default z-index of 1000 for Grid LoadPanel to ensure proper layering

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
packages/devextreme/js/__internal/ui/overlay/overlay.ts	Added zIndex property to OverlayProperties interface, implemented _handleZIndexOptionChanged method, refactored _updateZIndexStackPosition to support custom z-index, and added option change handler
packages/devextreme/js/__internal/grids/grid_core/m_utils.ts	Added BASE_LOAD_PANEL_Z_INDEX constant (1000) and applied it to LoadPanel options in Grid
packages/devextreme/testing/tests/DevExpress.ui.widgets/overlay.tests.js	Added three test cases covering custom zIndex initialization, changing from pool to custom zIndex, and resetting from custom to pool zIndex

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

packages/devextreme/js/__internal/ui/overlay/overlay.ts:1490

• Similar to the issue in _updateZIndexStackPosition, custom zIndex values should not be removed from the pool during disposal. The check should verify that the zIndex is pool-managed: if (this._isVisible() && !this.option('zIndex')) { zIndexPool.remove(this._zIndex); }

    if (this._isVisible()) {
      zIndexPool.remove(this._zIndex);
    }