car: a display density setting, so text and controls can grow in car apps

Size scales Gearslip's own screens but can't reach a hosted app, which
draws from the density it's handed. On a short screen those apps stay
small. Car display density, under Screen after Size, is From car or 160
to 240 DPI, and the video's resolution stays the same.

CarEnvironment.frame is what the display and hosted apps already read, so
the choice goes in there, once a session starts: the display and the apps
on it can't disagree mid-drive. Reconnecting or reopening the preview
applies a change. Phone mirroring keeps the car's own density, and the
cluster has its own.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

gearslip/src/main/res/values/strings.xml

@@ -189,6 +189,10 @@
     <string name="car_group_same">These are the same settings as Settings in the car. A change here shows there too.</string>
     <string name="car_open_on_connect">Open on connect</string>
     <string name="car_size">Size</string>
+    <string name="car_density">Car display density</string>
+    <string name="car_density_note">Larger text and controls, including in apps. Try 200 DPI with Size on Normal. Reconnect the car or reopen the preview to apply it. If controls clip, choose a lower DPI or From car.</string>
+    <string name="choice_density_car">From car</string>
+    <string name="choice_density_dpi">%1$d DPI</string>
     <string name="car_app_theme">App theme</string>
     <string name="car_dark_mode">Dark mode</string>
     <string name="car_buttons">Buttons</string>