bug#45915: 28.2; delete-char deletes two letters

[Tak Kunihiro]

>>   (buffer-substring (line-beginning-position) (line-end-position))
>> 
>> line 1 returns: "| 1 |"
>> line 2 returns: #("| 1 |" 1 2 (display (space :relative-width 1)) 3 4
>> (display (space :relative-width 1)))
>
> Those two 'display' properties are now displayed as a single stretch
> glyph, because two adjacent text properties with the same value are
> indistinguishable from a single one that spans all of the buffer
> positions.
>
> This is not a bug, this is how Emacs always worked.

I see. I understand that 'display' properties on an org-table matters.
I took a look for (org-table-align) and found that
`org-table-separator-space' defines the text properties as shown below.

org-table.el: (defconst org-table-separator-space
org-table.el:   (propertize " " 'display '(space :relative-width 1))
org-table.el:   "Space used around fields when aligning the table.
org-table.el: This space serves as a segment separator for the purposes of the
org-table.el: bidirectional reordering.")

Although I still do not understand the purpose of `:relative-width',
problem disappeared with following configuration.

  (with-eval-after-load "org-table"
    (setq org-table-separator-space " "))

I have an impression that default characters on
org-table-separator-space is problematic.