bug#30747: Emacs lacks a command to horizontally recenter

[積丹尼 Dan Jacobson]

Emacs has fancy commands to vertically recenter,
C-l runs the command recenter-top-bottom.

But alas no command to horizontally recenter.

All it has are the commands on
(info "(emacs) Horizontal Scrolling") Not good enough.

"It's just not fair." "Thin is in, fat is shat."

The future horizontal-recenter command (please implement) should keep
the cursor upon the same character (x), but just move the view screen ([
]) so that x is now in the center.

......[.......x..]...... BEFORE
.........[....x.....]... AFTER

Also at the end of (info "(emacs) Recentering")
add

     The above all refers to vertical recentering. For horizontal recentering
     see (info "(emacs) Horizontal Scrolling").

And on (info "(emacs) Horizontal Scrolling") add the above newly
implemented command, and at the bottom of course mention:

     The above all refers to horizontal scrolling/recentering. For vertical 
recentering
     see (info "(emacs) Recentering").


P.S.,
[..x.......]..... BEFORE
[..x.......]..... AFTER
i.e., nothing, is probably what should happen if there is no room to
pull from the left.
P.P.S., each "." represents around 10 characters.