Allow specifying supported extensions

One aspect that could also be covered by the project explorer is the support for extensions. There are many viewers, importers and exporters that support different extensions, and having a place to look up this, as a "feature matrix", may be helpful.

In fact, this could - as a first approximation - already largely be covered by the existing project explorer infrastructure. The supported extensions could be treated in a similar way as the existing tags:

{
  "name": "Example of a plugin for some authoring software",
  "type": ["plugin"],
  "outputs": ["glTF 2.0"],
   ...
   "inputExtensions" : ["KHR_lights_punctual", "KHR_draco_mesh_compression"],
   "outputExtensions" : ["KHR_lights_punctual", "KHR_materials_ior" ]
}

This would allow the existing search+filter structures to be used on these tags as well.

One could consider different levels of integration or organization for that. Roughly: One could pull out this aspect into a dedicated page, database, or search tool (for example, to show it on one page as an actual matrix, with the tools in the rows, the extensions in the columns, and ✔️ `s that indicate support). But regardless of the final presentation, I think that at least having this information in a central place in the project explorer database could be really useful.

Originally posted by @javagl in https://github.com/KhronosGroup/glTF-Project-Explorer/issues/122#issuecomment-944377531

Start by reading the existing project explorer infrastructure for tags, search, and filtering. Determine how extension metadata could be represented for inputs and outputs, and clarify whether the initial result should only support lookup and filtering or also provide a dedicated feature matrix. Done should mean the supported-extension information is centrally represented and usable through the agreed presentation.