MONGOID-5105 Allow block form in Mongoid::Association::EmbedsMany::Proxy#count (#5060)

* MONGOID-5105 Mongoid::Association::EmbedsMany::Proxy should allow block form for #count to make it congruent with #any?, #none?, #all?, etc.

Example:
Person.addresses.count {|a| a.country == "FR" }

I've also added additional tests for other methods.

* MONGOID-5105 Update docs

* MONGOID-5105 Fix specs on Ruby 2.3 and 2.4

* MONGOID-5105 - .create --> .create! in spec
- Update docs

* MONGOID-5105 improve spec robustness

* MONGOID-5105 separate the tests

* MONGOID-5105 remove Ruby 2.5+ requirement

Co-authored-by: shields <shields@tablecheck.com>
Co-authored-by: Oleg Pudeyev <code@olegp.name>

Author: 3 people

lib/mongoid/association/embedded/embeds_many/proxy.rb

@@ -102,12 +102,26 @@ def clear
           #
           # Use #size if you want the total number of documents.
           #
+          # If args or block are present, #count will delegate to the
+          # #count method on +target+ and will include both persisted
+          # and non-persisted documents.
+          #
           # @example Get the count of persisted documents.
           #   person.addresses.count
           #
+          # @example Get the count of all documents matching a block.
+          #   person.addresses.count { |a| a.country == "FR" }
+          #
+          # @example Use #persisted? inside block to count persisted documents.
+          #   person.addresses.count { |a| a.persisted? && a.country == "FR" }
+          #
+          # @param [ Object, Array<Object> ] args Args to delegate to the target.
+          #
           # @return [ Integer ] The total number of persisted embedded docs, as
           #   flagged by the #persisted? method.
-          def count
+          def count(*args, &block)
+            return _target.count(*args, &block) if args.any? || block
+
             _target.select { |doc| doc.persisted? }.size
           end