gdk/wayland: Mark matched settings from the portal as valid (3.24)

Commit e6209de9 added some checks on TranslationEntry.valid in order to figure out whether using the new font settings or the old g-s-d ones. However that's only set in the non-sandboxed case.

This makes sandboxed applications fallback to the old (and also non-existing with modern g-s-d) settings, possibly resulting in ugly defaults being picked.

Fix this by also marking TranslationEntry elements as valid when using the settings portal, precisely those entries that we are able to read and match with our own table.