install: explicitly install osk-sdl when needed (MR 2066)

This adds osk-sdl to the rootfs when --fde is set, or when building a
rootfs for the ondev installer. Ideally the ondev installer would
selectively install osk-sdl if the user opted for fde at runtime, but
I haven't found a straight forward way to enable that yet, and this
behavior here is no different than the current behavior (where osk-sdl
is always installed in the rootfs by way of depends= in pmos-mkinitfs).

For images that are built without --fde, osk-sdl won't be installed at
all in the rootfs, once the dependency is dropped from pmos-mkinitfs.

pmb/install/_install.py

@@ -806,6 +806,13 @@ def create_device_rootfs(args, step, steps):
     if locale_is_set:
         install_packages += ["lang", "musl-locales"]
 
+    # The ondev installer *could* enable fde at runtime, so include it
+    # explicitly in the rootfs until there's a mechanism to selectively install
+    # it when the ondev installer is running.
+    # Always install it when --fde is specified.
+    if args.full_disk_encryption or args.on_device_installer:
+        install_packages += ["osk-sdl"]
+
     pmb.helpers.repo.update(args, args.deviceinfo["arch"])
 
     # Explicitly call build on the install packages, to re-build them or any