bug#52973: Adding a few context-menu-mode commands

[Juri Linkov <juri@linkov.net>]

>> > I think once the user turns on context-menu-mode, all the modes that
>> > defined their context menus should automatically activate them.  There
>> > should be no need for any user customizations except turning on this
>> > mode.
>>
>> I would disagree, neither do I necessarily want all mode, nor do I
>> necessarily want to have the entries listed the default order.  In my
>> case I fix this by manually setting context-menu-functions to the
>> functions I want to use.
>
> Then we should allow users to opt out of the automatic activation of
> the context menus.  But the default should IMO be that they are
> activated in all modes.  After all, this mode wants to mimic "other
> applications", and those don't let you choose at all.  So I think
> users, especially newcomers, would expect that default.

The menu bar doesn't contain all available commands not to overwhelm the
users.  For the same reason, the context menu should stay reasonably short.
Otherwise, it might grow to 28-foot long, and everyone will be mocking
us for this.