[WC-3259] DG2: fix focus jump on filter controls

[yordan-st]

Pull request type

Bug fix (non-breaking change which fixes an issue)

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Description

Selecting Empty or Not empty in a DG2 text or number filter caused keyboard focus to jump to the top of the page, forcing keyboard users to re-orient after every operator change. This happened because the filter tried to focus a text input that was disabled in those cases. The fix prevents that focus attempt, so focus stays on the operator dropdown where the user already is.

What should be covered while testing?

• Verify that selecting Empty and Not empty in both text and number filters does not move focus away from the filter controls.
• Confirm keyboard-only flow works smoothly: open operator dropdown, choose operator, continue tabbing without losing place.
• Check that the value input is disabled for Empty/Not empty and enabled again for operators that require a value.
• Validate behavior in both directions: switch from value-based operator to Empty/Not empty and back again.