permission: handle end nodes with children cases

[RafaelGSS]

When two paths overlaps, the permission model returns a false negative cause the Node* doesn't contain an empty child ("") to consider it as an end node. For instance, if you call --allow-fs-read=/home/index.js,/home/index.json and call process.permission.has for both paths, it will return false for the index.js since it will create the following radix tree:

Child / Prefix: /home/index.js Child o Prefix: on End of tree: on End of tree(c): /home/index.js End of tree(c): 

and if you invert the parameters order: --allow-fs-read=/home/index.json,/home/index.js it will create an empty child for "/home/index.js" indicating "end node".

To handle it I've included a new parameter to Node*: is_leaf.

[nodejs-github-bot]

Review requested:

• @nodejs/security-wg

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/52411/

[nodejs-github-bot]

Landed in b38bc9f

[ruyadorno]

This commit does not land cleanly on v18.x-staging and will need manual backport in case we want it in v18.