log/slog: implement encoding.TextAppender for Level and LevelVar
For #62384
Change-Id: I10df580ef966e497ff8da4efde6dd6ce1ccb17b4
GitHub-Last-Rev:
5ad8e2e0473ff509b48e525f6c7328f6281766a3
GitHub-Pull-Request: golang/go#68855
Reviewed-on: https://go-review.googlesource.com/c/go/+/605056
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>