Ruby Bindings: Implement Enumerable for iterable collections

[jackorp]

Implement including Enumerable and the #each method for iterable collections.

This allows for example to iterate over a package query:

require 'libdnf5/base'

base = Base::Base.new
base.setup()

repo_sack = base.get_repo_sack()
repo_sack.create_repos_from_system_configuration()

rq = Repo::RepoQuery.new(base)
rq.filter_id('rawhide')

repo_sack.load_repos(Repo::Repo::Type_AVAILABLE)

query = Rpm::PackageQuery.new(base)
query.filter_provides("rubygem(httparty)", Common::QueryCmp_EQ)

query.each # Returns => #<Enumerator: ...>
query.each do |pkg|
  puts pkg.get_name
end
# Prints => rubygem-httparty
# And Returns => #<Rpm::PackageSet:0x00007f14d9ecd9a8 @__swigtype__="_p_libdnf5__rpm__PackageSet">

Related issue: #1780

[jackorp]

I have implemented #each for collections that I could find, I was just looking for the implemented "begin" method, so not sure if I missed any collections that are also iterable.

Other collections like Reldep or AdvisorySet do not have tests in Ruby so I have not extended them. I can take a stab at creating them if the tests are desired.

[jackorp]

There probably should be RETURN_SIZED_ENUMERATOR since we can get size beforehand, but the last argument to that macro is a function, that I am not quite sure how to supply or operate it in swig.

This should be a function that can be supplied for the RETURN_SIZED_ENUMERATOR:

VALUE size_for_enumerator(VALUE collection, VALUE args, VALUE eobj) {
    size_t size = $self->size();
    return SIZET2NUM(size);
}

See:
/usr/include/ruby/internal/intern/enumerator.h file in ruby-devel package
Inspired by Array from Ruby 2.7.0:
https://github.com/ruby/ruby/blob/v2_7_0/array.c#L2105
https://github.com/ruby/ruby/blob/v2_7_0/array.c#L2214