cmd/compile: optimize types.sconv
cmd/compile: optimize types.sconv

Now that symfmt is simpler, we can simply manually inline it into
sconv. Importantly, this allows us to avoid allocating a buffer +
writing a string + re-interning it when we don't need to qualify the
identifier.

Passes toolstash -cmp.

Updates #47087.

Change-Id: I47b57aef22301ba242556a645346f478f0c1a7d1
Reviewed-on: https://go-review.googlesource.com/c/go/+/333162
Trust: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
Run-TryBot: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@golang.org>

CAFxX/go,nawawi/go,cloudflare/go,nawawi/go,golang/go,CAFxX/go,cloudflare/go,cloudflare/go,CAFxX/go,golang/go,CAFxX/go,cloudflare/go,golang/go,golang/go,cloudflare/go,nawawi/go,nawawi/go,CAFxX/go,nawawi/go,CAFxX/go,golang/go,nawawi/go,nawawi/go,cloudflare/go,CAFxX/go,cloudflare/go,CAFxX/go,cloudflare/go,golang/go,golang/go,nawawi/go,golang/go