Feature: support custom font in ThemeData

[agufagit]

widgets under SettingsList always use default system font, doesn't use custom font

[yadaniyil]

Implemented in v3.0.0 — SettingsThemeData now exposes titleTextStyle, tileTextStyle, and tileDescriptionTextStyle fields. Pass a custom TextStyle to override fonts, sizes, and weights without subclassing.