[lldb/AppleSimulator] Always provide a -simulator environment

[lldb/AppleSimulator] Always provide a -simulator environment

Summary:
This commit is somewhat NFC-ish today as the environment of triples
is not considered when comparing s if one of them is
not set (I plan to change that).

We have made simulator triples unambiguous these days, but the
simulator platforms still advertise triples without the
environment. This wasn't an issue when the sims ran only on
a very different architecure than the real device, but this
has changed with Apple Silicon.

This patch simplifies the way GetSupportedArchitectureAtIndex
is implemented for the sim platforms and adds the environment.
It also trivially adds support for Apple Silicon to those
platforms.

Reviewers: aprantl

Subscribers: lldb-commits