Backport upstream fixes for Librem 5
Upstream backports:
- details: Clear newly added text-display before replaying log messages (0e59dd)
- text/tribar: Fix ply_boot_splash_hide () not clearing the terminal (c6a8cf)
- main: Retain splash on on_show_splash() and on_hide_splash() (e733f2)
- ply-device-manager: Fix bad assertion (7dcd1f)
Fixes plymouth crash when used on encrypted Librem 5 installations with osk-sdl and some minor annoyances when displaying boot logs via Vol- button.