Make theme's content_width available in XML-RPC

[koke]

To upload properly sized images, being able to access the theme's $content_width variable from XML-RPC would help

[nacin]

Patch also needs to check if $content_width isn't set and return 0. Probably also needs an int cast.

[josephscott]

(In [17663]) Expose the content width as a read only option via XML-RPC.

Fixes #17131 props koke, nacin

[westi]

As I said in IRC when this was originally being discussed.

I'm not sure why the theme's content width matters during image upload - what happens when I switch to a wider theme later?

Should the app not be working the media settings which have already been exposed?

[ptahdunbar]

We should standardize accessing the $content_width var instead of doing it manually everywhere. Enter, get_content_width() - #17130

[nacin]

Agreed on revert. I offered the patch before considering its usage. I was in IRC with westi and agreed then.

[ryan]

Revert per bug scrub.

[ryan]

In [18119]:

Revert [17663]. fixes #17131

[ramiy]

Related: #21256