bug#55692: 29.0.50; delete-selection-mode: Replace region only if set using the mouse

[Eli Zaretskii]

> From: Visuwesh <visuweshm@gmail.com>
> Date: Sat, 28 May 2022 23:03:51 +0530
> 
> Motivation: I often find myself annoyed by `delete-selection-mode' when
> using the keyboard since the region in Emacs does not translate to text
> selections in other applications.  On the contrary, I find myself
> wanting the behaviour of `delete-selection-mode' for regions set using
> the mouse.  Attached patch adds an user option to do that.

IMO, we shouldn't distinguish between the mouse and shift-selection
methods of defining the region.  So this feature, if accepted, should
also treat both methods of defining the region the same.