bug#65685: 29.1; Inconsistent behavior of quoted file name "/:~" across platforms

[Jim Porter <jporterbugs@gmail.com>]

To see this in action, run 'emacs -Q "/:~"' on both GNU/Linux and 
MS-Windows.[1] On GNU/Linux, this opens a dired buffer for the user's 
home directory. On MS-Windows, it opens a buffer for a new file named tilde.

According to the Emacs manual:

> ‘/:’ can also prevent ‘~’ from being treated as a special character
> for a user’s home directory. For example, /:/tmp/~hack refers to a
> file whose name is ~hack in directory /tmp.
I'd interpret this to mean that the MS-Windows behavior is correct. 
However, the example doesn't specifically say what should happen when 
the tilde comes immediately after the "/:". On the very rare occasions 
you might need it, you can always spell "a file named tilde in the 
current directory" like "/:./~".

This is relevant to some future Eshell changes I'm considering[2], where 
(I think) I'd like "/:~" to mean "the user's local home directory, even 
when default-directory is remote". In light of that, my selfish 
preference is that we keep the GNU/Linux behavior and standardize it 
across all systems. However, we could standardize the MS-Windows 
behavior instead; I'd then just have to call out the different Eshell 
semantics in the Eshell manual.

[1] You can see this inconsistency with other commands too, like "M-x cd 
RET /:~ RET".

[2] https://lists.gnu.org/archive/html/emacs-devel/2023-08/msg01244.html