DataGrid: prevent column resizing in band area (T1317039)

[anna-shakhova]

No description provided.

[Copilot]

Pull request overview

This PR fixes an issue where DataGrid columns could be resized from the band header area, which should not be allowed. The fix adds Y-coordinate checking to the column resizing logic to ensure resizing only occurs when the mouse is positioned within the actual resizable column header row, not in the band header area above it.

Changes:

• Modified the _getTargetPoint method to accept a Coordinates object (with both x and y) instead of just x coordinate, and added logic to check if the mouse Y position is at or below the top of the resizable column header
• Added proper null safety checks for _targetPoint throughout the codebase to handle cases where it may now be null when the mouse is in the band area
• Created a new functional.ts test file for functional column resizing tests and moved the existing visual test case, while adding a new test case specifically for the band area resizing prevention

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/devextreme/js/__internal/grids/grid_core/m_types.ts	Added new Coordinates interface to represent x and y coordinate pairs
packages/devextreme/js/__internal/grids/grid_core/columns_resizing_reordering/m_columns_resizing_reordering.ts	Updated _getTargetPoint to accept Coordinates object and check Y coordinate; added null safety in _setupResizingInfo; improved type annotations; refactored pointsByColumns method
packages/devextreme/js/__internal/grids/grid_core/column_fixing/m_column_fixing.ts	Updated overridden _getTargetPoint method signature to match base class changes
packages/devextreme/js/__internal/grids/grid_core/filter/m_filter_row.ts	Added null safety checks with optional chaining for _targetPoint accesses
packages/devextreme/testing/tests/DevExpress.ui.widgets.dataGrid/columnFixing.tests.js	Updated QUnit test calls to pass Coordinates object instead of just x coordinate
e2e/testcafe-devextreme/tests/dataGrid/common/columnResizing/visual.ts	Updated import paths and removed one test case (moved to functional.ts)
e2e/testcafe-devextreme/tests/dataGrid/common/columnResizing/functional.ts	New file containing functional tests for column resizing, including the moved test and a new test case for band area resizing prevention (T1317039)

[Copilot]

Pull request overview

Copilot reviewed 7 out of 16 changed files in this pull request and generated 2 comments.

[Copilot]

Incrementing with i += 1 is unnecessarily verbose. Use the standard i++ increment operator for consistency with JavaScript conventions.

Suggested change

	for (let i = 0; i < pointsByColumns.length; i += 1) {
	for (let i = 0; i < pointsByColumns.length; i++) {

[Copilot]

This test validates the Y-coordinate restriction when resizing from the band area, but there should also be a test verifying that normal column resizing (within valid Y bounds) still works correctly after this change.