Allow calling a private method with `self.`
Allow calling a private method with `self.`

This makes it consistent with calling private attribute assignment
methods, which currently is allowed (e.g. `self.value =`).

Calling a private method in this way can be useful when trying to
assign the return value to a local variable with the same name.

[Feature #11297] [Feature #16123]

ruby/spec,nobu/rubyspec,eregon/rubyspec,nobu/rubyspec,nobu/rubyspec,ruby/spec,eregon/rubyspec,ruby/spec,eregon/rubyspec