screen size: fix a car that reports the wrong size, and size the preview

Some head units report a size their screen isn't, then crop or squash the
picture onto it. Settings, on the phone and the car, now take the screen's
real size and how the car fits it. Crop keeps the UI and taps inside the
part the car shows, like a car's own margins. Squash draws for the real
shape and stretches it over the frame on the GPU, map apps included, so
the car's squash puts it back.

The car preview can also draw at the last car's size, this device's whole
screen, or a size typed in, for head units running Gearslip on their own.

gearslip/src/main/java/app/seb3thehacker/gearslip/car/CarSettingsScreen.kt

@@ -52,6 +52,8 @@ fun CarSettingsScreen() {
     val night by CarSettings.nightMode.collectAsState()
     val units by CarSettings.units.collectAsState()
     val navBar by CarSettings.navBarMode.collectAsState()
+    val screenSize by CarSettings.screenSize.collectAsState()
+    val screenFit by CarSettings.screenFit.collectAsState()
     val whatsNew by CarSettings.whatsNewAfterUpdates.collectAsState()
     val pipeAudio by CarSettings.pipeAudio.collectAsState()
     val speakDirections by CarSettings.speakDirections.collectAsState()
@@ -116,6 +118,22 @@ fun CarSettingsScreen() {
             units,
         ) { CarSettings.setUnits(it) }
 
+        // For a head unit that reports the wrong size and stretches the picture (issue #12).
+        ChoiceRow(
+            "Screen size (next connection)",
+            listOf<ScreenSize?>(null).plus(SCREEN_PRESETS).plus(screenSize).distinct()
+                .map { it to (it?.toString() ?: "From the car") },
+            screenSize,
+        ) { CarSettings.setScreenSize(it) }
+
+        if (screenSize != null) {
+            ChoiceRow(
+                "Fit to the screen",
+                listOf(ScreenFit.CROP to "Crop the edges", ScreenFit.SQUASH to "Squash to fit"),
+                screenFit,
+            ) { CarSettings.setScreenFit(it) }
+        }
+
         ChoiceRow(
             "Nav bar",
             listOf(
@@ -417,3 +435,8 @@ private fun StepButton(text: String, modifier: Modifier, onClick: () -> Unit) {
     }
 }
 
+/** Common car screen sizes; Settings on the phone takes any other. */
+private val SCREEN_PRESETS = listOf(
+    ScreenSize(800, 480), ScreenSize(1024, 600), ScreenSize(1280, 480), ScreenSize(1280, 720),
+    ScreenSize(1440, 540), ScreenSize(1920, 720), ScreenSize(1920, 1080),
+)