driver: Always bind zle-line-finish and use it instead of accept-*

Special handling for cursor imprint or partial path highlighting
is needed in more cases than accept-*. For example when accepting
a line from isearch, no accept-* widget is invoked.

The proper way is to use zle-line-finish.

Trumps #259.
Fixes #284.

highlighters/main/test-data/path_prefix2.zsh

@@ -31,7 +31,7 @@
 # Related to path_prefix.zsh
 
 BUFFER='ls /bin/s'
-WIDGET=accept-line
+WIDGET=zle-line-finish
 
 expected_region_highlight=(
   "4 9 default"    # /bin/s