Don't create children until after we check if element is wrapped by a component

[Corecii]

roact-template/src/lib/init.lua

Lines 398 to 412 in 7205657

	local children = {}
	for name, child in pairs(template.children) do
	children[name] = elementFromTemplate(Roact, child, callSelectors, nameSelectors)
	end
	local props = applySelectors(Roact, template, children, callSelectors, nameSelectors)
	local element
	if props[Wrap] then
	element = Roact.createElement(props[Wrap], {
	template = RoactTemplate.componentFromTemplate(Roact, template),
	})
	else
	element = Roact.createElement(template.class, props, children)
	end

Currently if an element is wrapped with a component it creates all of its children just to throw them away.

Creating children first is only necessary because ChangesCallback mutates the existing props and children dicts. Children should not be read. Props has reasonable use-cases for reading e.g. darkening default background color. If we have ChangesCallback return the new props it wants to set then we preserve all existing functionality and we can compute children after ChangesCallback is ran. This would allow Wrapped elements to not compute their children until their template is created.