Display issues for login language switcher

[rtibbles]

Observed behavior

Incorrect overflow observed:

Modal positioned incorrectly:

Expected behavior

Language switcher should not overflow onto second line, modal should not be causing unnecessary page scroll.

User-facing consequences

Odd experience on many people's first use of Kolibri

Steps to reproduce

Go to the login page on desktop.
See the languages overflowing.
Click change language, see the modal awkwardly positioned.

Context

There has been recent work to update the language switcher (mostly in the context of the setup wizard) that may have contributed to this, but it seems likely that there has been an unintended interaction with other changes in 0.17 as well.

Fixing this should also make sure not to cause regressions in the setup wizard language switching display.

[rtibbles]

Fixed in #12448