bug#5042: bug#9917: bug#5042: bug#9917: 24.0.90; Make `goto-line' consistent with the line number from the minibuffer

[Juri Linkov]

>>> So a new command and keystroke seems warranted.  How about...
>>> `M-g M-v'?   (The mnemonic is "goto visual line".)
>>
>> Or to add a new key to narrow-map 'C-x n' where a new key could be:
>>
>>   C-x n g         go to narrowed line
>
> Perhaps both?  The keystroke makes sense in both contexts -- as a
> variation on `M-g M-g', and in the group of narrowing keystroke.

I've added a more localized key binding 'C-x n g',
but still not sure about the global 'M-g' key bindings.
Here are some possible variants:

1. Bind 'M-g v' to goto-line-relative, while leaving 'M-g g'
   bound to goto-line that currently uses absolute line numbers
   (btw, this fact should be mentioned in its docstring);

2. Re-bind 'M-g g' to goto-line-relative as many asked to do
   with the reasoning that 'M-g g' should use by default the
   same numbering scheme as is displayed by display-line-numbers-mode;

3. Leave the existing 'M-g g' bound to goto-line, but allow changing
   the numbering scheme using a prefix arg and a user option.
   Or another idea: maybe it should depend on whether
   display-line-numbers-mode is enabled or not?
   When display-line-numbers-mode is enabled, then use
   relative line numbers that are displayed on the left side (WYSIWYG).