[BUG] Documenting a set() command with PARENT_SCOPE (or other flags) generates incorrect documentation

[AutonomicPerfectionist]

Describe the bug
Documenting the following command:

set(MyString "String" PARENT_SCOPE)

Documents the variable MyString as a List with the initial values String PARENT_SCOPE

Expected behavior
We should probably check for the PARENT_SCOPE flag, remove it from the type
and default value calculations, and flag it in the generated documentation.
I think adding a note that it sets in the parent scope should be sufficient.

I believe this affects other set() flags like CACHE