fail a package that includes font_size in it's preferences

[keith-hall]

There was recently a discussion on Discord whereby someone was unable to change the font size on specific syntaxes. It initially seemed related to sublimehq/sublime_text#1551, but it turned out that the package contained a syntax specific settings file with font_size declared. As Sublime Text's Preferences menu -> Settings - Syntax Specific opens the Default preferences and the User syntax specific preferences side by side, it wasn't easy to find that the package declared font_size in it's syntax specific preferences without looking at the package directly.

I propose that packages which set font_size in their preferences should fail the review.
Maybe it'd be a good idea to also have a warning if syntax specific preferences are used, for the human reviewer to check if the readme contains some tips relating to it, to avoid similar problems with other "hidden" preferences.

[FichteFoll]

As a note to myself (and others): there should be other settings that should never be modified.