doc/go1.20: add runtime, runtime/trace, and runtime/pprof release notes
This change adds release notes for the "Runtime" section and updated
some of the release notes for runtime/trace and runtime/pprof after I
looked at the full list of runtime-related changes.
For #54202.
Change-Id: Id1395f4e6e02d3fcc248855ca98ad0ee26cae574
Reviewed-on: https://go-review.googlesource.com/c/go/+/454075
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Robert Griesemer <gri@google.com> Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
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