LEAP API for getInfo and getPaths combined.

So right now when we query getPaths we get a set of paths, which we inevitably will also need to getInfo on as we rarely just need to know a path, and usually need to know both a path and the value of the field at the path.

Right now we do getPaths and then getInfo on the path as a separate action, which leads to race conditions where the paths from getPaths go stale before we manage to getInfo on them. This leads to dumps of into the viewer log where we're requesting getInfo on an old path.

I'd like a new API for getPaths something like:

LLWindowAPI
op="getSubtree"

//optional
under=/path/to/some/element. (default should be `/`)

The result should be all elements and their info data that are descendants of under. Note that this would be recursive so doing /a/b/ should return /a/b/child1 and /a/b/child1/subchild

We can work with this structure being a tree or a list, whichever is easiest, though if you do treat this as a tree instead of a list, it might be possible to resolve https://github.com/secondlife/viewer/issues/5779 (partially) as well with this syntax.

Test Plan

1. Setup outleap-repl
2. Call getSubtree on LLWindowAPI and we should get a full tree from root.