filtering to show installed plugins

[richlv]

It might be useful to add a plugin filter to only show installed plugins.
If I want to find out which plugins I have installed, it requires quite a lot of scrolling and checkbox spotting currently.

[Don-vip]

We could have several tabs, it's common in administration UIs (Jenkins, Sonarqube, etc):

-------------------------------
| Installed | Available | All |
-------------------------------

[stoecker]

Doesn't match existing UI of JOSM. A filter or checkbox would be more like what we do elsewhere.

[Don-vip]

Indeed, it would be more consistent.

[Don-vip]

In 13799/josm:

fix #16220 - filter plugins by installation state

[Klumbumbus]

When I choose installed plugins only and then type in the filterbox below the installation filter is ignored and all plugins matching the string are displayed. Then when I switch to only available plugins, all available plugins are displayed while the text in the filterbox remains but is ignored. If possible both filter mechanisms should respect each other as currently this leads to inconsistent displays:

[Don-vip]

In 13802/josm:

fix #16220 - fix plugin filter

[Don-vip]

In 15587/josm:

see #16220 - add translation context for "Available" plugins, to distinguish from "Available" tools in toolbar