Hi,

In Org code, we have various places where we depend (optionally) on
third-party packages. The packages are typically loaded using `require'
and report the usual error about missing library if the third-party
package is not installed.

Such situation is _almost_ OK, except some scenarios when the feature
name we in `require' is not the same with the actual package name.
Inexperienced users may easily be confused by such errors.

In the attached patch, I am introducing a new macro that can be used
instead of `require' as the following:

(org-require-package 'skewer-repl "skewer-mode")

The macro calls `require' and if it fails, displays error/warning saying

"`this-command' failed to load required package \"package name\""

It will assist users about the actual third-party package name to be
installed.

WDYT?

While writing a patch, I also noticed
`org-cite-csl--barf-without-citeproc' doing similar job.
Should we just use the new macro instead?

Also, https://github.com/bard/mozrepl ob-js backend is no longer
supported. I am wondering if we should remove it.