chore: restructure `Platform`

[skaldarnar]

Contains

Restructure the Platform utility class and splits out OS and Arch as separate enums.

Loosely based on #708.

How to test

Nothing should change based on this PR.

Outstanding before merging

Gather opinions on whether we should split this up for more flexibility in modeling (that we probabyl don't need) or rather go the opposite way and have a more restrictive enum regarding supported platforms. See my discussion notes in the PR: https://github.com/MovingBlocks/TerasologyLauncher/pull/714/files#diff-9c6b18468622aa7d6c00cd8b643c7fd04df9b5155cad37526aa99686fd925056R20-R38