UI/UX suggestion: Parts catalogue filter

[Kavaeric]

Also another x-post at the suggestion of a user on the Discord:

Browsing for parts in the catalogue could probably be made much more robust and flexible if a filtering system was implemented. Part categories are nice but it can be difficult to remember whether parachutes were in...landing? Or aerodynamics?

The existing improvements in clarity over KSP1 are appreciated, such as the size radius class and subheaders, but with the implication of many more parts included in the game versus KSP1 had in stock as time goes on, as well as modders pitching in new parts, a built-in filter system feels like a sensible addition. It should also alleviate the strain for those who jump into sandbox and feel overwhelmed with the number of parts, an existing problem in KSP1 even without DLC and mods—helping them to hide everything that is or isn't of a certain size class or fuel type (especially if multiple fuel types are to be added in the future beyond the basic LF/O/Xenon) would better help them navigate vehicle design as well as the kinds of choices one makes when putting together a rocket (ISP vs thrust, for example). This would also help curtain some other concerns the dev team might have, such as engine archetypes for newcomers.

A side suggestion is also to allow for players to configure filters based on existing parts, such as clicking the Terrier engine to find other liquid fuel engines of its size; or even to have a specific button for certain parts like engines that will direct the user to appropriately-sized fuel tanks of the correct resource.

[Kavaeric]

Some modders in the KSP2 modding Discord were interested by the proposal and I decided to clean up the concept a little to be clearer. It's still mostly fragmentary and incomplete but otherwise more detailed than above. The dev team may find this useful too, though I figure there are more pressing matters in the game than this.