Search backend: clean up `Count` on `query.Basic`
Created by: camdencheek
This does three things:
- Removes the unused
AddCount
- Renames
basic.GetCount
tobasic.Count
- Makes
basic.Count
return a well-typed integer so the string doesn't need to be parsed by every caller
Stacked on #34156
Test plan
Should not change any behavior. Depending on tests.