Fix overrideable hand ToolCapabilities and range

[cx384]

Solves #15740

To avoid confusion, notice:
selected_item is the item selected in the hotbar, ("" if empty)
hand_item is the overwritten hand ("" by default).
tool_item/playeritem/punchitem is what should be used for getToolCapabilities (getWieldedItem returns this)

getToolCapabilities needs both tool_item and hand_item as a fallback.

Callbacks and node placement still only uses selected_item.

To do

Ready for Review.

How to test

• Like explained in the issue, try e.g.

core.register_item("default:hand", {
	type = "none",
	range = 20,
	tool_capabilities = {
		groupcaps = {
			crumbly = {times={[1] = 0.1, [2] = 0.1, [3] = 0.1}, uses = 0, maxlevel = 1},
			cracky = {times={[1] = 0.1, [2] = 0.1, [3] = 0.1}, uses = 0, maxlevel = 1},
		}
	}
})

core.register_chatcommand('hand', {
	func = function(name, param)
		local player = core.get_player_by_name(name)

		local handitem
		if param == 'reset' then
			handitem = ''
		else
			handitem = 'default:hand'
		end

		local inv = player:get_inventory()
		inv:set_size('hand', 1)
		inv:set_stack('hand', 1, ItemStack(handitem))
	end
})

• See that it works while wielding nothing, and while e.g. a node