revert commit 1fe19578c2 which changed `anchor()` values to `position-area`.
I'm not sure what compelled me to do that change initially, except the easier to understand syntax. Hopefully it wasn't important.
But oddbird polyfill expects `anchor()` values, which it converts to pixel values for positioning.
This commit only renames things, changes no logic. Any mention of "book", "view", or "mode" is renamed in relation to "spreads".
The AnchoredBox.jsx file is renamed to Anchored.jsx
Extra icons are deleted, and the remaining ones are renamed.
Gazook89