gh-143070: Use "+" instead of "!" in automatically generated tkinter widget names...

gh-143070: Use "+" instead of "!" in automatically generated tkinter widget names (GH-151975)

The "!" prefix has a special meaning in the tag expressions of the
canvas and text widgets ("!", "&&", "||", "^" and parentheses), so an
automatically generated widget name could not be used as a tag.  "+" has
no special meaning there, nor in option database patterns or Tcl lists,
and a user is very unlikely to start an explicit name with it.