Elide file names in the middle again

Elide file names in the middle again

In ye olden days, filenames were elided on the right. This prevented
seeing the filename extension and any suffix style text the user
included in the filename (e.g. "myfile 1", "myfile 2" and so on).

In 97f49347482519b9ad53b7596d7462e68b7c2e14, this was changed to elide
in the middle, fixing both problems and bringing Dolphin into Jakobs'
Law style consistency with MacOS Finder and Windows Explorer, and
possibly other file managers too.

However it worsened the situation for users who name their files such
that most of the information was on the left. After some complaints, it
was changed in 99cf24c03def1c0722ba8dbd86a27b9dbc521f43 to right-elide
again, but excluding the filename extension.

Unfortunately user complaints have continued. At this point it's clear
that nothing will satisfy everyone due to diversity of file naming
styles. In such a situation, Jakobs' Law consistency with the rest of
the industry is the best solution short of making it configurable,
which has its own drawbacks.

Accordingly, return to middle-elision.

BUG: 497664
CCBUG: 404955
FIXED-IN: 25.04.0