Quantity.__format__ with unicode or console does not typeset the unit correctly #14398

Description

As noted by @olebole in #14393, if one formats a Quantity with unicode or console format, the result is bad: the denominator gets put under the value. I think this was an oversight when @eerovaher introduced allowing __format__ to take format as an argument in #13050 -- although the underlying problem is likely that the formatters use line breaks which do not keep pieces together (see below).

Expected behavior

The unit should stay together.

How to Reproduce

import astropy.units as u
q = 10*u.m/u.s
print(f"{q:unicode}")
10.0  m
 ─
 s

print(f"{q:console}")
10.0  m
 -
 s

The problem really seems to be due to the use of line breaks in the unit; one would have to collect this and typeset it differently.

q.unit.to_string('console')
' m\n -\n s'

Versions

Linux-5.10.0-20-amd64-x86_64-with-glibc2.31
Python 3.9.2 (default, Feb 28 2021, 17:03:44)
[GCC 10.2.1 20210110]
astropy 5.3.dev513+gab61aa73a