kcms/kfontinst,fonts: move to top level category

Reason for the change

This is primarily to alleviate BUG 493174 somewhat, so that instead of the Font Management page ending up with 5 columns, it now has just 4, and the font preview becomes much less cramped. I'm mainly tackling that issue in !4707 now.

The "font" category also has just two entries, "Fonts" and "Font Management", which is really clumsy when trying to open the font management page.

The weights were tweaked so that it goes Wallpaper -> Fonts -> Font Management -> (Color and Themes).

kcm_fonts is moved up a level to occupy the same place as the Text & Fonts category is in right now, and kfontinst is moved to System as (a) that's the most fitting place, semantically, and (b) it doesn't have to be next to Fonts.

Original commit message(s)

• kcms/kfontinst,fonts: move to top level

  The weight is also modified such that the order is: Wallpaper -> Fonts -> Font Management -> Themes

  For kfontinst, this leaves more horizontal space for the font preview. Right now the font preview is never wide enough due to its UI ending up with 5 columns: System Settings top level, the "font" category, the group list, the font list, and the font preview. This has proven to be frustrating.

  For kcm_fonts, it's mainly because without kfontinst that category is now useless. As for why it should go to top level ("appearance") and not "themes", it's because it's similar to the wallpaper KCM, and that in "themes" it feels out of place. Almost every other page in "themes" use a "there is one option to configure, here's a pretty list of candidates to choose from", you can manage these themes if you want to.

  (Night Light is also out of place by this standard, yes.)

Test plan

I changed the categorization and opened System Settings to see the pages in the right places.

Screenshots or screen recordings

Before	After (kfontinst)	After (kcm_fonts)

Bugs fixed

BUG: 493174

(Although kfontinst still needs a new layout to truly stop it from itself needing 3 columns, this change alone should be enough to take kfontinst back to the amount of space it enjoyed during the Icon View days.)