encoding/csv: update and add CSV reading benchmarks
encoding/csv: update and add CSV reading benchmarks

Benchmarks broken off from https://golang.org/cl/24723 and modified to
allocate less in the places we're not trying to measure.

Updates #16791

Change-Id: I508e4cfeac60322d56f1d71ff1912f6a6f183a63
Reviewed-on: https://go-review.googlesource.com/30357
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

cloudflare/go,goodlang/good,nawawi/go,codestation/go,nawawi/go,suncycheng/go,linux-on-ibm-z/go,Cofyc/go,goodlang/good,CAFxX/go,Cofyc/go,ImJasonH/go,polyverse-security/go,linux-on-ibm-z/go,Cofyc/go,suncycheng/go,linux-on-ibm-z/go,derekmarcotte/go,nawawi/go,akutz/go,linux-on-ibm-z/go,linux-on-ibm-z/go,momchil-velikov/go,akutz/go,ImJasonH/go,derekmarcotte/go,polyverse-security/go,goodlang/good,golang/go,momchil-velikov/go,momchil-velikov/go,goodlang/good,akutz/go,polyverse-security/go,momchil-velikov/go,nawawi/go,akutz/go,CAFxX/go,nawawi/go,vsekhar/elastic-go,josharian/go,CAFxX/go,linux-on-ibm-z/go,suncycheng/go,polyverse-security/go,CAFxX/go,ImJasonH/go,golang/go,ImJasonH/go,vsekhar/elastic-go,polyverse-security/go,golang/go,CAFxX/go,vsekhar/elastic-go,cloudflare/go,golang/go,codestation/go,vsekhar/elastic-go,cloudflare/go,CAFxX/go,Cofyc/go,josharian/go,Cofyc/go,nawawi/go,suncycheng/go,polyverse-security/go,nawawi/go,akutz/go,akutz/go,christopher-henderson/Go,derekmarcotte/go,Cofyc/go,linux-on-ibm-z/go,goodlang/good,vsekhar/elastic-go,cloudflare/go,momchil-velikov/go,ImJasonH/go,polyverse-security/go,codestation/go,golang/go,cloudflare/go,josharian/go,derekmarcotte/go,ImJasonH/go,josharian/go,vsekhar/elastic-go,akutz/go,codestation/go,Cofyc/go,cloudflare/go,josharian/go,ImJasonH/go,momchil-velikov/go,cloudflare/go,codestation/go,golang/go,codestation/go,CAFxX/go,Cofyc/go,akutz/go,momchil-velikov/go,codestation/go,nawawi/go,linux-on-ibm-z/go,suncycheng/go,cloudflare/go,goodlang/good,derekmarcotte/go,derekmarcotte/go,goodlang/good,vsekhar/elastic-go,suncycheng/go,suncycheng/go,derekmarcotte/go,josharian/go,golang/go,derekmarcotte/go,goodlang/good,polyverse-security/go,CAFxX/go,codestation/go,ImJasonH/go,josharian/go,suncycheng/go,golang/go,josharian/go,vsekhar/elastic-go,momchil-velikov/go