[javac] Add @MaxLength annotation for limiting lengths of string parameters

[SamCarlberg]

Useful for eg OpModes, where names have a maximum length

Also includes validations for values in opmode annotations like @Autonomous(name = "..."); name, group, and description all have maximum allowable lengths

[PeterJohnson]

Seeing as these don't result in runtime errors (we'll just truncate), should these be warnings instead of errors?

[SamCarlberg]

Warnings would clutter the IDE logs and be ignored. My goal with the compiler plugins is to catch code that's obviously incorrect and code that won't function as the user expects; opmode string length checks fall into the second category, since the code that you write won't match what you see in practice