Add preferCountWhere rule

[calda]

As suggested in #1933, this PR adds a new preferCountWhere rule to prefer count(where:) over filter(_:).count calls in Swift 6.0+:

- planets.filter { !$0.moons.isEmpty }.count
+ planets.count(where: { !$0.moons.isEmpty })

- planets.filter { planet in
-     planet.moons.filter { moon in
-         moon.hasAtmosphere
-     }.count > 1
- }.count
+ planets.count(where: { planet in
+     planet.moons.count(where: { moon in
+         moon.hasAtmosphere
+     }) > 1
+ })

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.14%. Comparing base (f36187b) to head (8f27d07).
Report is 3 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #1939      +/-   ##
===========================================
- Coverage    95.18%   95.14%   -0.04%     
===========================================
  Files          137      138       +1     
  Lines        25094    25199     +105     
===========================================
+ Hits         23885    23976      +91     
- Misses        1209     1223      +14     

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[miguel-jimenez-0529]

Nice!

[nicklockwood]

Amazing! 😍