Inject measure funcs directly into UiSurface

## What problem does this solve or what need does it fill?

Atm we set measure funcs indirectly using the `ContentSize` component. If a new measure is required for some content the content's update system has to wrap the measure inside a NodeMeasure enum which is then wrapped inside an Option. In `ui_system_layout` we `take` it out the option and pass it taffy which stores it in its `node_context_data` slotmap. This seems unnecessarily overcomplicated.

## What solution would you like?

Instead the systems that update the measure funcs could just retrieve `UiSurface` and call its `update_node_context` method to inject the measure directly.