In preparation for adding the new span creation methods, `startSpan` and
`startActiveSpan`, this PR adds `name` to `spanContext`. Over time we
are going to be moving away from `span.description`, and this is the
first step to get there.

For now, `name` is just an alias for `span.description`, and is only
added so that users can do something like so relatively easily:

```js
const span = span.startChild({ name: 'NAME HERE' });
```

[Gitflow] Merge master into develop

#8794)