This patch:
- reverts the sizes that use addition (theme.defaultFont.pointSize) to hardcoded integers, otherwise the font sizes on the login and lock screens don't match (regardless of the user's or sddm's kdeglobals settings)
- hardcodes the pointSize in KeyboardLayoutButton.qml, SessionManagementScreen.qml (the "Unlocking Failed" and "Login Failed" notifications) so they would match the other font sizes on the lock screen (in case the user decides to change font sizes)
- hardcodes the pointSize in KeyboardButton.qml and SessionButton.qml for the sake of completeness
- raises the font size of the "Start New Session" button on the lock screen (to match the size of the login/unlock buttons)
- raises the artist and track font sizes in the media controls section (so they would be more in tune with the field above and the button below them, no pun intended)