Change the relative time format to `LONG`

The `SHORT` format, which abbreviates relative time as 'x min.
ago,' presents an accessibility issue for screen readers like
TalkBack. TalkBack announces this as 'x minimum. Ago', and the
dot after "min" is treated as period and causes a full-stop.

Attempts to directly modify TalkBack's pronunciation of this
text have proven difficult. Given the ample space available in
the user interface, using abbreviations isn't necessary.
Switching to the `LONG` format ('x minutes ago') would resolve
this accessibility problem while also making the interface
clearer for all users.

Bug: 318323722
Change-Id: I42ba960bd8d5d8fc8a9cb895ecf24c56dab6d2c4