[restructure] Simplify and flatten caching

[pzuraq]

This is some of the precursor work to the new API:

1. Simplify the cell cache in general
2. Wrap columns and rows in proxies that add meta properties
3. Yield value cell column row as described in the new API
4. Have CollapseTree return the list of parents, which allows us to
   correctly figure out selection state in tree tables (more work and tests
   on that coming in future PRs)
5. Create a "row wrapper" component. This is necessary for wrapping the
   rows in proxy objects, since it should be done after VC has done its
   work in order to remain stable, but before we yield to the tr because
   we don't want to complicate the tr logic (its been a struggling
   point on the refactor branch)