Added return T on invoke for MutableProperty0
Added return T on invoke for MutableProperty0

In some cases like when using 'inputScalar' under 'ImGui' `MutableProperty0#invoke` is called more often the `MutableProperty0#get`. This will lead to "null" in the user input box when using MutableProperty0 over an Array.
kotlin-graphics/imgui,kotlin-graphics/imgui,jovr/imgui