[FR] Add `ddd` function

[michaelrog]

Global function to "dump, die, and debug" —

Will require a DumpDieDebug Exception. We should give special treatment to that Exception class in the handler, whereby instead of showing the typical error/code frame for the actual ddd() call, we show the dump instead (using Symfony VarDumper?).

Should take variable number of args — ddd($thing1, $thing2, ...)