Jetpack AI: Add Chrome built-in AI summarization API as the model for AI excerpt

[vianasw]

Fixes #

Proposed changes:

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Does this pull request change what data or activity we track or use?

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• Go to '..'

[github-actions]

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[github-actions]

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 3 files.

File	Coverage	Δ%	Δ Uncovered
projects/js-packages/ai-client/src/chrome-ai/suggestions.ts	0/48 (0.00%)	0.00%	18 💔
projects/js-packages/ai-client/src/chrome-ai/factory.ts	0/46 (0.00%)	0.00%	7 💔
projects/plugins/jetpack/extensions/blocks/ai-assistant/ai-assistant.php	0/96 (0.00%)	0.00%	1 ❤️‍🩹

Full summary · PHP report · JS report

_{Coverage check overridden by I don't care about code coverage for this PR Use this label to ignore the check for insufficient code coveage. .}

[vianasw]

I don't care about code coverage for this PR – This is an experimental feature that we want to test internally first.