InputMessageContent model. Valid subtypes: InputTextMessageContent, InputLocationMessageContent, InputVenueMessageContent, InputContactMessageContent, InputInvoiceMessageContent
@type t() :: ExGram.Model.InputTextMessageContent.t() | ExGram.Model.InputLocationMessageContent.t() | ExGram.Model.InputVenueMessageContent.t() | ExGram.Model.InputContactMessageContent.t() | ExGram.Model.InputInvoiceMessageContent.t()