[lldb] Add Apple simulator platforms to lldbplatform.py

This just adds the simulator platforms to the lldbplatform enumerations
and the respective test decorator.

The platform names for the simulator are just the SDK names since D85537, so
that's why we are not using LLDB's usual platform names here (e.g., SDK =
"iphonesimulator" vs LLDB platform ="ios-simulator").

Also removes the duplicate platform enumaration in lldbplatformutil.py.

Reviewed By: JDevlieghere

Differential Revision: https://reviews.llvm.org/D89694