Add file formatter exclusion by paths

Adding the php.formatter.excludeFromFile option we could exclude files (as Prettier already does, for example, with the .prettierignore file).

This is very interesting when you only want to format the new files and keep the olds ones intact.

Thanks for a great suggestion again! We'll take a look at that as well.

It would be ideal if this exclusion were directly implemented in VS Code, but it seems that this will not happen soon. https://github.com/microsoft/vscode/issues/176946