Clarify documentation about the interaction of recordError and setStatus

Currently the docs aren't prescriptive enough, which can make switching between tracing backends more difficult.

For example, does `recordError` imply:

1. An error occurred during the span, and the span should be considered errored as well, regardless of calls to `setStatus`
2. An error occurred during the span, and the span should be considered errored as well, unless `setStatus` was called with `OK`
3. An error occurred during the span, but the overall status of the span should not be considered errored (unless `setStatus` is also called with `Error`)
4. An error occurred during the span, and as a library we don't attribute any specific semantic meaning to the corresponding status of the span
5. Something else?

Review the existing documentation for recordError and setStatus, then compare the stated behavior with the tracing semantics expected when switching backends. Done means the documentation explicitly defines how recordError affects span status, including the interaction with setStatus and the applicable exceptions.

Written by the indexing model from the issue text.