stats.lua: clip lines with ${term-clip-cc}

Use the property introduced in bf025cd289 to clip the lines of stats.lua
with accurate unicode width detection and considering --msg-module and
--msg-time. This allows removing the term ellipsis functions.

Also use script-opts-append instead of script-opts in the docs so
script-opts in mpv.conf, which could change keybindings, are not
overriden.

DOCS/interface-changes/stats-term-clip.txt

@@ -0,0 +1,2 @@
+remove `stats-term_width_limit` script-opt
+add `stats-term_clip` script-opt