Speed up logic to validate member and extension exists

[chrjorgensen]

Changes

This PR is an alternative to PR #1826 and will keep the check for member existence.

Instead of using QSYS2.SYSPARTITIONSTAT to retrieve the member information, which could be slow on small server with many, many members, the code introduces a new SQL table function <tempLib>.GETMBRINFO to get the information for the specific member. API QUSRMBRD is used by GETMBRINFO behind the scenes.

Checklist

• [x] have tested my change