dillon1000/react

DevTools: merge element fields in TreeStateContext (#31956)

Stacked on https://github.com/facebook/react/pull/31892, see commit on
top.

For some reason, there were 2 fields different fields for essentially
same thing: `selectedElementID` and `inspectedElementID`. Basically, the
change is:
```
selectedElementID -> inspectedElementID
selectedElementIndex -> inspectedElementIndex
```

I have a theory that it was due to previously used async approach around
element inspection, and the whole `InspectedElementView` was wrapped in
`Suspense`.