Arrow navigation always prioritizes parent DataGridView control regardless of what child control is focused.

[JayashreeSF3546]

Fixes #6361

Proposed changes

• Added an early check in ProcessKeyPreview for WM_KEYDOWN / WM_SYSKEYDOWN and WM_SYSCHAR.
• Skipped DataGridView preview handling when the key message targets a hosted child control instead of the DataGridView itself.
• Preserved existing behavior for the active EditingControl to avoid edit-mode regressions.

Customer Impact

• Fixes an issue where arrow keys intended for hosted child controls could be intercepted by the parent DataGridView.
• Improves keyboard navigation behavior for controls hosted inside DataGridView.Controls.

Regression?

• No

Risk

• Low — the change is scoped to key preview handling and preserves existing behavior for the DataGridView and its EditingControl.

Screenshots

NA

Test methodology

• Added tests for arrow key messages targeted at hosted child controls.
• Verified that normal DataGridView arrow-key behavior remains unchanged when the grid itself is the target.
• Verified that existing edit-mode behavior is preserved for the EditingControl.

Accessibility testing

N/A — no UI or accessibility surface change.

Test environment(s)

• Windows 11
• .NET SDK: 11.0.100-preview.3.26170.106

Microsoft Reviewers: Open in CodeFlow