runtime,hash/maphash: make tests use less memory

runtime,hash/maphash: make tests use less memory

Use a list + sorting instead of a map to keep track of collisions.
Should save a fair amount of memory.

Change-Id: I7b48cdb5f7060d12ebbb950d56b5c479f131c027
Reviewed-on: https://go-review.googlesource.com/c/go/+/574275
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: qiulaidongfeng <2645477756@qq.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Keith Randall <khr@google.com>