Add missing dependency to 'trash' applet meson.build

[Gcec21]

Description

link_libpanelenum is not currently listed in applet_trash_deps. Although this builds just fine on systems using meson with ninja, this will result in build failure on systems that use meson with samurai, outputting the following error message:

In file included from .. /src/panel/applets/trash/trash_plugin.h:14,
		from /src/panel/applets/trash/trash_plugin.h:15:
../src/plugin/panel/plugin.h:16:10: fatal error: budgie-enums.h: no such file or directory 

This error can be especially problematic on distros like Alpine Linux which only ship samurai in the main repositories. Apparently, this is due to a difference in how ninja and samurai schedule build edges (see Meson Issue #9937 & samurai differences from ninja), which consequently requires dependencies to be specified more explicitly.

Therefore, this pull requests adds link_libpanelenum into applet_trash_deps, to ensure that Budgie can be built and compiled on any system.

Also, somewhat related to the pull request, I noticed that link_libpanelenum is not actually linked to libpanelenum. I refrained from modifying this in case there was a functional reason for it, but I'd happily create another pull request for it if there's none.

Submitter Checklist

• Squashed commits with git rebase -i (if needed)
• Built budgie-desktop and verified that the patch worked (if needed)

[serebit]

LGTM, thanks!