Library QoL improvements

[sonnyp]

Since the library has grown so much we should add QoL improvements to make it more pleasant and appealing. We already made some very nice improvements:

• [x] https://github.com/workbenchdev/Workbench/pull/522 @bragefuglseth
• [x] https://github.com/workbenchdev/Workbench/pull/678 @Diego-Ivan

The Library is currently (ab-)using AdwPreferencesWindow and related widgets. This was good to build something quickly but is now limiting us in what we can do. So let's stop using Adw preferences widgets.

• [x] https://github.com/workbenchdev/Workbench/pull/949 @BharatAtbrat
• [x] Stop using AdwPreferencesPage @BharatAtbrat (we don't need that anymore)
• [x] Stop using AdwPreferencesGroup @BharatAtbrat (simples Gtk.Label will do the trick)
• [x] Stop using AdwPreferencesRow @BharatAtbrat

https://github.com/workbenchdev/Workbench/pull/958

Once that's done we can make further improvements

• [x] https://github.com/workbenchdev/Workbench/pull/950 @BharatAtbrat (makes search more prominent)
• [ ] Add a Category filter
• [ ] Add a language filter
• [ ] Hide the category headers on search or when the category filter is active

For the category and language filter we can take inspiration from https://github.com/workbenchdev/Workbench/issues/510