Change block interaction override to crouch keybind instead of shift

[hazelmeowing]

"Block interaction override" being the key you hold to place a block while looking at something that would normally do something else, currently it is always mods.shift which can be problematic. For example I use shift for sprint and toggle sprint, meaning whenever I want to use this I toggle whether I am running, which is bothersome (additionally, some people might not have mods.shift bound for anything else, which would make this very unnatural). I don't think it is necessary to add a special keybind for this, and changing it to "crouch" will be familiar for people coming from Minecraft.

I did notice however there is dropFromHand which also checks mods.shift to decide whether to drop a whole stack or not, currently I have not changed this as I checked in Minecraft and for some reason this is always shift unlike block interaction overriding, I do feel this is an inconsistency and I obviously don't think Cubyz should seek to be inconsistent just because Minecraft is, but I am unsure whether it would be better to add a new keybind for this or make it "crouch"

[IntegratedQuantum]

We used to have a key for this (which got removed in the refactoring of #2144)

I do agree that we should have this remappable, but I do not think that this is the right approach. Tying it to crouching, a completely unrelated activity.

Also I do like the modifiers in the sense that now there is a clear and fixed list of key modifiers you can check, instead of having to query a random key.
So maybe we could just introduce a new entry in the modifers struct that is remappable.