Improved fixable tasks

[veewee]

Q	A
Branch	master
Bug fix?	no
New feature?	no
BC breaks?	no
Deprecations?	no
Documented?	no
Fixed tickets	#786

This PR limits the amount of boilerplate that is needed for creating fixable task results and drops the need for a custom formatter.

Example:

if (!$process->isSuccessful()) {
    return FixableProcessResultProvider::provide(
        TaskResult::createFailed($this, $context, $this->formatter->format($process)),
        function () use ($arguments): Process {
            $arguments->add('--fix');
            return $this->processBuilder->buildProcess($arguments);
        }
    );
}