feat(vertexai): Migrate to `AI` and add GoogleAI support #21823

Job	Run time
Build the SDK	8m 59s
(Firestore) Node.js and Browser (Chrome) Tests	24m 6s
(bulk) Node.js and Browser (Chrome) Tests	5m 14s
Firestore Integration Tests (persistence)	5m 48s
Firestore Integration Tests (memory)	4m 50s
(Auth) Node.js and Browser (Chrome) Tests	2m 48s
	51m 45s

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