[ty] IDE: add support for `object.<CURSOR>` completions (#18468)
This PR adds logic for detecting `Name Dot [Name]` token patterns,
finding the corresponding `ExprAttribute`, getting the type of the
object and returning the members available on that object.
Here's a video demonstrating this working:
https://github.com/user-attachments/assets/42ce78e8-5930-4211-a18a-fa2a0434d0eb
Ref astral-sh/ty#86
