[tz] Support for Etc/GMT -style zones ids with partial hours

[Paul Eggert]

On 10/21/20 10:12 AM, Neil Fuller via tz wrote:
> The Stock Android settings UI, starting with Android Pie (9.0), allows
> users to select from the fixed "Etc/GMT-5" style identifiers from TZDB

How does that work at the user level? I have an Android 10 phone (build 
QQ1A.200105.032), and couldn't see these UI options under either 
"Settings>System>Date & time>Time zone" or "Clock>⋮>Settings>Home time zone" 
(these have different UIs).

> The current Etc/GMT[+-] zone identifiers in TZDB only cover whole hour
> offsets. There are various places that use 30 minute offsets, and a few
> that use 45/15 minute offsets [2].

I suppose we could add IDs for non-hour offsets currently in use. I worry, 
though, that there will be more odd offsets outside the civil-aviation 
application area, such as the offsets that various astronomical observatories 
use (as Steve Allen mentioned).

In GNU/Linux the way to solve this problem is to use a TZ setting like 
TZ='<+0545>-5:45' for Nepal (or TZ='NPT-5:45' for older POSIX). Does this work 
for Android? If so, I suggest going that way. If not, perhaps POSIX TZ support 
should be added to Android; that shouldn't be hard, and would improve 
functionality and compatibility in other areas too. If it couldn't be done for 
Android it could at least be done for the Clock app.