[llvm] [docs] Strengthen our quality standards and connect AI contribution policy to it (PR #154441)

[Reid Kleckner via llvm-commits]

https://github.com/rnk commented:

I had pending comments, sorry these are stale, I wrote them last week. It makes more sense for me to send these as one update, and then focus on new feedback post project council meeting.

https://github.com/llvm/llvm-project/pull/154441