cmd/compile,runtime: add indirect key/elem to swissmap

cmd/compile,runtime: add indirect key/elem to swissmap

We use the same heuristics as existing maps.

For #54766.

Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest-swissmap
Change-Id: I44bb51483cae2c1714717f1b501850fb9e55a39a
Reviewed-on: https://go-review.googlesource.com/c/go/+/616461
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>