feat: middle mouse to select blocks in build mode

[sekwah41]

No description provided.

[Gegy]

Ooh, thanks so much for implementing this! This is a much needed feature that we've left for too long 😄
I'm a bit hesitant to introducing the client-authoritative item picking here; if you're up for switching the approach, that would be fantastic :)

[Gegy]

Although this is what creative mode does, and we do have filtering here (thanks for adding that in 😅), it would be really nice to avoid this kind of client -> server item request. Particularly, from experience of how flimsy this can be in creative mode already - and how dangerous sending an ItemStack client->server can be in general, for all the kinds of weirdly nested/recursive structures that can be constructed.

In the latest snapshots, this is something Vanilla actually handles totally server-driven - I think it shouldn't be too tricky to do a similar kind of thing, where the client just sends a "hey, pick this block for me" packet and the server does all the logic and tells the client about what item it gets. (Block entity serialisation on the client also is a bit of a scary one 😅)

[sekwah41]

oh thats a good point and wouldnt be too tall a task to implement, Ill take a look later at switching it over to a blockpos rather than item stack target. Luckily the rest of the code can be kept the same :)