Use a value object for vector data instead of an array

Thank you @kim.pepper - I'm assuming this was in review since the MR is there and not in draft? - I added one minor issue for someone to fix.

More importantly, this is a breaking change, so I'm not sure this is possible to actually implement before 2.0.0. I'll just verify that with Scott, since he's the lead on VDB + AI Search.

2.0.0 is however most likely released in autumn, meaning that we will have Symfony integration first in 3.0.0 most likely, based on their timeline, so we would have to have time to start preparing all changes for an eventual move in 2.0.0 and then do the full move in 3.0.0.

Thanks for the contribution! Yeah makes sense to me re version and timeline. Is there any reason not to also have ::getDimensions() given the eventual Symfony AI Platform compatibility plan?

@kim.pepper sounds like you are making a new VDB Provider so BTW once you have in place we can reference from AI module homepage + add to docs https://project.pages.drupalcode.org/ai/1.2.x/providers/matris/ - helps also keep track of maintainers to contact with breaking changes/coordinated releases particularly while we are still in experimental.

I added a vector document and an interface for a vector store.

Updating the title to better reflect the direction.