runtime: make getStackMap a method of stkframe
This places getStackMap alongside argBytes and argMapInternal as
another method of stkframe.
For #54466, albeit rather indirectly.
Change-Id: I411dda3605dd7f996983706afcbefddf29a68a85
Reviewed-on: https://go-review.googlesource.com/c/go/+/424515
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Austin Clements <austin@google.com>
Auto-Submit: Austin Clements <austin@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>