ResponseFactory::createFromException already had support for arbitrary
exceptions, but Router was so far only using it for HttpExceptions,
leaving other kinds of exceptions uncaught.
In addition to catching all exceptions and generating an appropriate
JSON response for them, this patch introduces the ErrorReporter
interface, with an MWErrorReporter implementation which calls
MWExceptionHandler::rollbackMasterChangesAndLog(). This is how uncaught
errors are handled for requests coming in via api.php, so it seems
appropriate to use the same approach for requests coming in via
rest.php.
Bug: T285984
Change-Id: I0605a7693821ef58fac80ab67f51a742556a37fd
