Add `ignore` and `ignore_deserialize` properties to `URI::Params::Field`

[Fijxu]

Feature Request

JSON::Serializable and YAML::Serializable contain this field properties to ignore serialization/deserialization, URI::Params::Serializable could also have them to use them with something like this (crystal spec):

struct A
  include URI::Params::Serializable

  property name : String
  property age : Int32?

  def initialize(@name : String, @age : Int32? = nil)
    after_initialize
  end

  @[URI::Params::Field(ignore: true)]
  property msg : String?

  def after_initialize
    @msg = "Hello " + name
  end
end

person = A.new("Vasya", 30)
person.msg.should eq "Hello Vasya"

person.to_www_form.should eq "name=Vasya&Age=30"

A.from_www_form(person.to_www_form).msg.should eq "Hello Vasya"

Currently, with that small spec code, A.from_www_form(person.to_www_form).msg.should eq "Hello Vasya" will actually equal to "name=Vasya&age=30&msg=Hello+Vasya" since property @msg is not ignored.

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[straight-shoota]

There are two pending PRs, submitted within the past two days:

• Add URI::Params::Field(ignore:), ignore_serialize, ignore_deserialize #17029 by @trypsynth
• Add URI::Params::Field ignore options #17037 by @RoySerbi

The feature isn't very complicated, so naturally the patches are pretty similar.
There are some notable differences:

• The specs from #17029 seem more complete: they validate that ignore_deserialize: true still serializes, for example.
• In #17029, ignore_serialize accepts runtime expressions (same as JSON and YAML).

So #17029 looks like the superior choice to me.