Added static methods to create ArgumentBuilders directly in the BrigadierCommand class

[4drian3d]

Until now, to create a command with several brigadier nodes required a lot of boilerplate, otherwise, a compilation error arises

final LiteralCommandNode<CommandSource> rootNode = LiteralArgumentBuilder.<CommandSource>literal("command")
  .then(RequiredArgumentBuilder.<CommandSource, String>argument("argument", StringArgumentType.word())
    .executes(context -> {
      // command execution
      return Command.SINGLE_SUCCESS;
   })
  ).build();

With this pull request, the creation of a brigadier command would be significantly simplified, eliminating the unnecessary use of generics

final LiteralCommandNode<CommandSource> rootNode = BrigadierCommand.literalArgumentBuilder("command")
  .then(BrigadierCommand.requiredArgumentBuilder("argument", StringArgumentType.word())
    .executes(context -> {
      // command execution
      return Command.SINGLE_SUCCESS;
   })
  ).build();

In addition, it adds extra validations that Brigadier does not perform, such as improper use of spaces in the name of a LiteralCommandNode.

These methods may seem unnecessary, but for a complex node with several subnodes, it would be quite useful since normally one would do a static method doing exactly the same thing.