This commit updates gen-postmortem-metadata.py to re-export
the v8dbg_class_JSFunction__shared__SharedFunctionInfo
constant.

See: https://github.com/nodejs/node/pull/25852
Change-Id: I60f39c96f3f22d6f10ec38b0af3c975908c7b7f2
Reviewed-on: https://chromium-review.googlesource.com/c/1450144Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59334}