bug#39902: 28.0.50; Marking in dired with active region

[Juri Linkov]

> I see our different views as of the same right and value.  And the use
> case (who uses marking commands with an active region at all?) is a
> corner case.  I don't mind about the default as long as there is a new
> option.

There is nothing new here.  Mathematicians have been fighting that battle
for centuries until invention of the special notation to differentiate
including and excluding endpoints using either a square bracket or
a reversed parenthesis to indicate inclusive/exclusive intervals:

https://en.wikipedia.org/wiki/Bracket_(mathematics)#Intervals
https://en.wikipedia.org/wiki/Interval_(mathematics)#Including_or_excluding_endpoints

The most recent development is still ongoing in new programming languages.
For example, in the initial versions of Rust there were only
exclusive ranges, so e.g.

  for i in 1..3

yields only 1 and 2, but not 3, like the region mark command in Dired now.

But later Rust versions added inclusive ranges as well with special syntax:

  for i in 1..=3

that yields 1, 2 and 3.

Please see more examples at
https://doc.rust-lang.org/edition-guide/rust-2018/data-types/inclusive-ranges.html

So Dired could do the same and support both range types using a new option
'dired-mark-inclusive'.

> I would rather want to discuss what else should be done
> (behavior of other marking commands etc, should we change
> `dired-mark-if', etc.

I think `dired-mark-if' should respect that option too.