go/parser: track depth in nested element lists

go/parser: track depth in nested element lists

Prevents stack exhaustion with extremely deeply nested literal values,
i.e. field values in structs.

Fixes #69138
Fixes CVE-2024-34155

Change-Id: I2e8e33b44105cc169d7ed1ae83fb56df0c10f1ee
Reviewed-on: https://go-internal-review.googlesource.com/c/go/+/1520
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
Reviewed-by: Russ Cox <rsc@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/611238
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>