Mutable properties for classes in Common

[nlbuescher]

Currently a system exists in codegen to generate setters for a selected whitelist of properties in ImGui classes. One notable property missing is ImGuiIO.configFlags, and modification of ImGuiStyle's properties is probably another good use case, but the question comes to mind: At what point might it be better to tweak the generation to make properties mutable based on whether they're const rather than explicitly following a whitelist?

[Dominaezzz]

Not many of them are const and I don't know if some properties are only meant to be mutable internally. So I settled with an on-demand whitelist and moved on.