Change should_skip_file to not require the MetadataWrapper

[sk-]

Today should_skip_file is an instance method and hence requires the metadata wrapper, which in turn requires to parse the code.

However, the two rules defining this method, only use the file name and the config.

It would be ideal if we could change it so that the check could be performed without having to parse the code.

For example to speed up the linting I want to just use the _source (I know it's private now) checking if it matches a very simplified regex (note: this regex would be autogenerated).