Implement Suspense

[AdamRamberg]

Implement Suspense, simlar to how Suspense in React / Solid. The challenge with this issue is that the fallback component will need to have a higher prio being mounted than the children on the Suspense will have to be rendered.

[AdamRamberg]

One idea is to add the following to FiberNode:

• A bool called isInSuspenseTree - when using the suspense component, that corresponding FiberNode and all under it will be flagged.
• An intcalled suspensionCount - which is incremented every time an ancestor is added to the fiber tree and / or rendered. It's decremented when an ancestor is mounted.
• A bool called isSuspenseComponent - flagging what FiberNode is a suspense component.

We could then use a combination of a signal and an effect in the suspense component to trigger hooks etc. for when a sub tree is suspending or not.