8056: completion relevance consider if types can be unified r=JoshMcguigan a=JoshMcguigan
This PR improves completion relevance scoring for generic types, in cases where the types could unify.
### Before
![pre-could-unify](https://user-images.githubusercontent.com/
22216761/
111338556-
46d94e80-8634-11eb-9936-
2b20eb9e6756.png)
### After
![post-could-unify](https://user-images.githubusercontent.com/
22216761/
111338598-
4e005c80-8634-11eb-92e0-
69c2c1cda6fc.png)
changelog feature improve completions
Co-authored-by: Josh Mcguigan <joshmcg88@gmail.com>