Mark Blender ESCN exporter as deprecated

[tetrapod00]

Closes #8196.
Alternate or complement to #10064.

This PR adds a warning to each page under Blender ESCN exporter that the blender plugin is depreacted in Godot 4.x. Personally, I believe even calling the plugin "deprecated" is promising too much, since it has not been maintained at all since Godot 4.0, and is producing shader errors for all tested Godot 4 versions (see #8196 (comment)). "Deprecated" implies that the plugin functions in the current Godot version, but is not receiving updates.

Some combination of this PR and #10064 (which removes these pages entirely, except for a stub redirect page) should be applied to all Godot 4.x docs versions. I see three options:

1. Apply this PR to 4.4 and cherrypick it to all 4.x docs versions (or as far back as we cherrypick).
2. Apply Remove Blender ESCN exporter pages #10064 to 4.4, and apply this PR to all previous 4.x docs versions (or as far back as we cherrypick).
3. Apply Remove Blender ESCN exporter pages #10064 to 4.4, and cherrypick it back to all previous 4.x docs versions (or as far back as we cherrypick).

Option 1 seems like the wrong choice to me. I don't think carrying these docs pages forward to future Godot 4.x versions makes sense. The plugin is unmaintained, unsupported, and does not even export at all since Blender version 4.0. The plugin does not work at all in Blender 4.2, which is the current Blender LTS version as of Godot 4.3.

Option 2 makes sense to me, since it corrects the problem for future 4.x docs versions and keeps the existing docs pages for anyone still relying on them.

Option 3 also makes sense, and is my preferred solution. The Blender addon has in practice been unmaintained and unsupported since Godot 4.0. It should have been marked deprecated since Godot version 4.x, and perhaps not included in the Godot 4.x docs at all.

[fire]

We have a similar problem with the collada importer.

[tetrapod00]

We have a similar problem with the collada importer.

There's just a single reference to that addon. Made a PR: #10074

[fire]

I think using the same strategy as the collada plugin would work here. Not sure which one that is on your list

[tetrapod00]

There is no exact analogue to the the Collada plugin strategy, since this plugin also has several actual pages of docs.

#10064 is approved by two docs maintainers, so I'd suggest you review that and see if it's acceptable?

The current state of that PR removes the pages except for a stub, calls the plugin "unmaintained and unsupported", but does not call the plugin "deprecated", since it was not officially deprecated. It also manually links to an older version of the full docs, in case someone still needs them.

[skyace65]

Closing this as #10064 was merged