Deps: add webui-popover (npm)

This commit adds webgui-popover v. 1.2.18 as npm dependency to ILIAS 10.

= Usage =

ILIAS/UI

= Reasoning =

The library is used to create popovers in the UI-framework. This applies to the
initial Popover component, as well as to other components, such as Filters, that
use the Popover component.

= Maintenance =

There are 26 contributors to the library. The last commit to the library is 8 years
old, as well as the last released version. Last opem issue is from Oct '21, as well
as the last closed issue. Last closed PR is from 2023. The open issues seem to be
either feature requests or rather specific bugs.

It seems as if the development of the library has stopped, be it because its
feature complete, be it because interest vanished.

= Links =

NPM: https://www.npmjs.com/package/webui-popover
GitHub: https://github.com/sandywalker/webui-popover
Documentation: https://www.npmjs.com/package/webui-popover?activeTab=readme

= Alternatives =

There are plenty of alternatives to this library in the JS library space. Also,
the HTML standard itself has gotten facilities to create popovers, although they
are not enough to replace this library.

= Assessment =

The library has served us well for quite some time now. We most probably would not
add it as a new library now, due to the state of its maintenance. It still seems to
be reasonable to accept it for ILIAS 10 now, so we can move on with the release and
testing. We should definitly look for alternatives for ILIAS 11, most probably a
custom implementation for vanilla HTML/JS. Dependending on the complexity of the new
solution and the state of the ILIAS 10 release, we could then decide to replace the
library.

package.json

@@ -19,7 +19,7 @@
     "linkifyjs": "^4.1.3",
     "moment": "^2.29.4",
     "tinymce": "^7.3.0",
-    "jstree": "^3.3.16"
+    "webui-popover": "^1.2.18"
   },
   "devDependencies": {
     "@rollup/plugin-node-resolve": "^15.3.0",