update copilot-api and send `event_content` (#4928)

* update copilot-api

* bump @vscode/copilot-api to ^0.2.19 in chat-lib

Agent-Logs-Url: https://github.com/microsoft/vscode-copilot-chat/sessions/90d7cd27-17c0-485e-9c91-26a3be612848

Co-authored-by: joshspicer <23246594+joshspicer@users.noreply.github.com>

* Add event_content to RemoteAgentJobPayload

ref https://github.com/microsoft/vscode-copilot-chat/pull/4819

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>