bug#61652: 28.2; Read-only mode and View mode

[Bernd Rellermeyer]

I have the following scenario:

1. View a buffer in View mode.
2. Turn off Read-Only mode, e.g. by pressing `C-x C-q`.
3. Turn on Read-Only mode and View mode again, eg. by pressing `C-x
C-q`-
4. Exit View mode by `View-exit`, e.g. by pressing `e`.

Now the buffer is in Read-Only mode. In my opinion it should be
writable. The reason is the variable `view-old-buffer-read-only`, which
is set on entering View mode (`view--enable`) to the (old) value of
`buffer-read-only`. But in my scenario, the value of `buffer-read-only`
is already the new one, as set in `read-only-mode`.

I think the solution is to reset `read-only-mode` to nil in the specific
branch of `read-only-mode` and depend on the fact that it is set to t in
`view--enable`:

```
  (cond
   ((and (not buffer-read-only) view-mode)
    (View-exit-and-edit)
    (setq-local view-read-only t))              ; Must leave view mode.
   ((and buffer-read-only view-read-only
         ;; If view-mode is already active, `view-mode-enter' is a nop.
         (not view-mode)
         (not (eq (get major-mode 'mode-class) 'special)))
    (setq buffer-read-only nil)
    (view-mode-enter))))
```


In GNU Emacs 28.2 (build 1, x86_64-apple-darwin18.7.0, NS appkit-1671.60 
Version 10.14.6 (Build 18G95))
 of 2022-09-12 built on builder10-14.lan
Windowing system distributor 'Apple', version 10.3.2299
System Description:  macOS 13.2.1

Configured using:
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