[Suggestion] Add exception type for command execution failure

[Marcono1234]

Currently the only existing exception type is CommandSyntaxException, wich is also used by Command.run(CommandContext<S>).

However, in most (if not all) cases exceptions thrown by run are unrelated to the syntax of the command, they are rather related to the state of the application (e.g. the state of the Minecraft world). Therefore it might be good to add a new separate exception type, such as CommandExecutionException and add it as thrown exception type to run.
Assuming that this would be a checked exception type, such a change might cause backward incompatibilities in some situations.

Additionally the following changes could be done:

• Remove CommandSyntaxException from the throws clause of run
• Remove CommandSyntaxException constructor without input and cursor parameter; 'real' syntax exceptions should have enough context to specify input and cursor values

This would require larger refactoring for dependent projects because they are currently throwing CommandSyntaxException inside run, and maybe there are edge cases where throwing CommandSyntaxException from run is reasonable.