Sparse documentation on `Span.isRecording`

The current documentation about Span.isRecording is:

```
/// Returns true if this `Span` is recording information like events, attributes, status, etc.
var isRecording: Bool { get }
```

Does that mean a `Span` implementation is allowed to drop all the events on the floor? Who consumes that property? Should clients read it before they try to attach massive amounts of data to the `Span`?

Start from the documentation for Span.isRecording and determine what the property means for dropping events, who consumes it, and whether clients should check it before attaching large amounts of data. Update the documentation to answer those questions clearly and verify the revised wording in the relevant documentation output.

Written by the indexing model from the issue text.