Idea: Events to pause rendering and resume rendering from APL

[cursork]

We suffer from significant flicker due to every WC, WS rerendering. Some of the UIs we want to support are complex with many objects. I propose RenderStop and RenderContinue events to build up the initial state of the UI, but not render. Two seconds of flicker is worse than waiting two seconds.

NB This will result in issues using WG for dynamic properties, as the components will simply not be available until RenderContinue. I think this is reasonable, and we can choose to error if we want.

The context is looking at some applications using ⎕WC and seeing that, even locally, there is flicker.