Fix on screen keyboard french layout and "flag" key

The 1st commit fixes the lack of french layout in the onscreen keyboard on Buster, which is a regression since Stretch (debian bug #926452). It is a direct cherry pick of an upstream commit.

The 2nd commit fixes the "flag" key that was introduced by the new onscreen keyboard (it is not present in Stretch), which shows a menu listing the available layouts. But moving the pointer over this menu closes the keyboard (debian bug #926453). This cherry picks one upstream commit and backports another one.