fix: supportsXCommands() methods now use SubcommandMappings

[BenSegal855]

This PR changes the behavior of the supportsMessageCommands() and supportsChatInputCommands() methods on the subcommand class. Previously, these both would always return true since the methods inherited from the Command class just check for the existence of a messageRun() or chatInputRun() method. Since both methods are implemented on the Subcommand class, the type guards would always return true. This PR instead determines the output of these methods by checking if a messageRun or chatInputRun property was provided on any of the subcommands in the parsedSubcommandMappings array. These changes were tested using commands with all combinations of having a messageRun, having a chatInputRun, having both, having groups, and not having groups. Test commands can be found in this gist.