Write new formatting engine

PSSA2 currently only has an analyzer. It should also have a formatter.

In particular, the API should allow objects to implement an abstract class that doesn't emit diagnostics, but instead contributes edits to a formatting buffer.

Rules should be able to provide an implementation for this also by implementing an API that provides an instance of the required abstract class.

Requirements are:

• Run as many formatters over the script as it can at once
• When formatters want to overwrite the same extent, the largest wins
• Attempt to run until no more formatters have edits to make, up to some maximum number of runs
• Formatters should reuse the rule configuration system

Empieza leyendo el analizador existente y el sistema de configuración de reglas, y después determina cómo podría encajar una API de formatter junto a ellos. Se considera terminado cuando se admiten instancias de formatter, ediciones concurrentes con un comportamiento de «gana la mayor superposición», ejecuciones repetidas hasta un límite y la reutilización de la configuración de reglas.