kcms/fonts: Improve accuracy and clarity of subpixel rendering info tooltip

I found the original tooltip to not be entirely accurate and too wordy. Some issues with it:

• TFT is a type of LCD
• It doesn't mention OLEDs which often have weird subpixel layouts (WBGR/RWBG/etc on LG OLEDs, triangular layout on QD-OLEDs, my Dell XPS 13 Plus has an even weirder layout)
• Percieved font quality can be improved even if the selection doesn't match exactly

Although I'm not sure how the I18n system works here, hopefully I haven't broken anything.