runtime: add a map growth benchmark
runtime: add a map growth benchmark

Updates #19931
Updates #19992

Change-Id: Ib2d4e6b9b89a49caa443310d896dce8d6db06050
Reviewed-on: https://go-review.googlesource.com/40978
Run-TryBot: Josh Bleecher Snyder <cdc248cc4d32e4fbfe04e45228163bcecd48a0b9@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>

Cofyc/go,CAFxX/go,Cofyc/go,Cofyc/go,vsekhar/elastic-go,cloudflare/go,CAFxX/go,derekmarcotte/go,cloudflare/go,Cofyc/go,derekmarcotte/go,akutz/go,josharian/go,nawawi/go,polyverse-security/go,derekmarcotte/go,cloudflare/go,Cofyc/go,derekmarcotte/go,CAFxX/go,cloudflare/go,golang/go,josharian/go,cloudflare/go,codestation/go,nawawi/go,nawawi/go,codestation/go,golang/go,golang/go,christopher-henderson/Go,CAFxX/go,akutz/go,golang/go,ImJasonH/go,polyverse-security/go,derekmarcotte/go,akutz/go,CAFxX/go,vsekhar/elastic-go,codestation/go,codestation/go,codestation/go,nawawi/go,akutz/go,golang/go,akutz/go,vsekhar/elastic-go,ImJasonH/go,polyverse-security/go,polyverse-security/go,Cofyc/go,vsekhar/elastic-go,golang/go,codestation/go,cloudflare/go,CAFxX/go,josharian/go,polyverse-security/go,akutz/go,nawawi/go,codestation/go,cloudflare/go,derekmarcotte/go,nawawi/go,golang/go,nawawi/go,codestation/go,ImJasonH/go,vsekhar/elastic-go,derekmarcotte/go,josharian/go,vsekhar/elastic-go,Cofyc/go,josharian/go,ImJasonH/go,ImJasonH/go,cloudflare/go,derekmarcotte/go,CAFxX/go,akutz/go,polyverse-security/go,CAFxX/go,vsekhar/elastic-go,ImJasonH/go,josharian/go,golang/go,nawawi/go,akutz/go,ImJasonH/go,josharian/go,ImJasonH/go,polyverse-security/go,polyverse-security/go,josharian/go,Cofyc/go,vsekhar/elastic-go