Fix: aborted steering prompt incorrectly terminates agent response (#297020)

* Initial plan

* Fix: reset yieldRequested when aborted steering prompt is removed from queue

Co-authored-by: connor4312 <[email protected]>

* Fix: propagate yieldRequested reset to extension host when steering prompt is aborted

Co-authored-by: connor4312 <[email protected]>

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: connor4312 <[email protected]>