lang/nim: Update version 2.0.0=>2.0.2

• Move pkg-message to SUB_FILES and replace hard coded PREFIX [1]
• Convert pkg-mesage to UCL format [1]

Changelog: https://nim-lang.org/blog/2023/12/19/versions-1618-202-released.html

PR: 275942
Approved by: submitter is maintainer, portmgr(blanket) [1]