Bug 286207

For the InlineIterator classes, we have first/previous/next/last traversal methods, but a) It's not clear what order this is (it's LTR order). b) We need multiple orders, and this only provides one of them. Specifically, we need to be able to iterate inline boxes: 1. In source order, for painting. 2. In LTR/RTL order, for logical movement. 3. In coordinate increasing/decreasing order, for hit testing and other geometrical operations. Note: I believe InlineIteratorLogicalOrderTraversal is supposed to provide (1), though it might need to be used in more places (we don't paint correctly). We might want to rethink what order we use as the backing store, but in any case we need multiple traversal methods and we need to have clear names to distinguish what they each do.