Document Compartment availability and OOM limitations

[mhofman]

What is the Problem Being Solved?

Compartments enables sandboxing of code, but since all compartment code still runs in the same agent, it inherits some limitations that should be documented:

• Code running in a compartment can deny availability to any other code executing in that agent, e.g. by going into an infinite loop.
• Because the JS spec doesn't guarantee that OOM panics the agent, code exported by a compartment can be attacked by another compartment setting it up for OOM failures (either stack or heap). This can result in an integrity compromises instead of an availability one.

Description of the Design

Update Endo and SES documentation to make these limitations clear.

Security Considerations

Better documentation of security assumptions