runtime: clean up escaping in tests
There are several tests in the runtime that need to force various
things to escape to the heap. This CL centralizes this functionality
into runtime.Escape, defined in export_test.
Change-Id: I2de2519661603ad46c372877a9c93efef8e7a857
Reviewed-on: https://go-review.googlesource.com/c/go/+/402178
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Austin Clements <austin@google.com>
Auto-Submit: Austin Clements <austin@google.com>