runtime: clarify finalizer semantics for tiny objects
runtime: clarify finalizer semantics for tiny objects

This change clarifies that a finalizer is not guaranteed to run,
not only for zero bytes objects but also tiny objects (< 16bytes).

Fixes #46827

Change-Id: I193e77f6f024c79110604f86bcb1a28b16cf98ec
Reviewed-on: https://go-review.googlesource.com/c/go/+/337391
Run-TryBot: Changkun Ou <1d6e1cf70ec6f9ab28d3ea4b27a49a77654d370e@changkun.de>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Joedian Reid <454f26308bdf67a957daa60c4ad294a9b7c3fcbc@golang.org>
Reviewed-by: Michael Knyszek <4473450dc5c88f06e1fb787f303d7805ec2aee65@google.com>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go