DATAMONGO-2059 - Favor collection.countDocuments() over collection.count() which will be removed.

[christophstrobl]

This commit switches from simple collection.count(), operating on potentially false collection statistic, to countDocuments() using an aggregation for accurate results.
The transition required query modifications at some points because $match does not support $near nor $nearSphere but requires $geoWithin using $center or $centerSphere which does not support $minDistance (see SERVER-37043).
$geoWithin further more does not sort results by distance, but this fact can be ignored when just counting matches.

ℹ️ The change is a requirement for upgrading to the next driver version that no longer supports collection.count().

Examples:

// before
{ "location" : { "$near" : [-73.99171, 40.738868], "$maxDistance" : 1.1 } }

// after
{ "location" : { "$geoWithin" : { "$center" : [ [-73.99171, 40.738868], 1.1] } } }

// before
{ "location" : { "$near" : [-73.99171, 40.738868], "$minDistance" : 0.1, "$maxDistance" : 1.1 } }

// after
{ "$and" :[ 
    { "$nor" :[ { "location" :{ "$geoWithin" :{ "$center" :[ [-73.99171, 40.738868 ], 0.01] } } } ] },
    { "location" :{ "$geoWithin" :{ "$center" :[ [-73.99171, 40.738868 ], 1.1] } } } 
] }

[mp911de]

That's merged and polished now.

[doronlevari]

Can we get this one merged into 2.2.X? It doesn't seem THAT major and we're in a huge need for this, Mongo is totally crapping out on us when using "count"