Shared Symbol intrinsic

[kriskowal]

Currently, Compartments share globalThis.Symbol with the start compartment, the realm global environment. Consequently, if the host has any symbols that are not recognized by SES’s permits, Lockdown will fail.

We should instead create a separate Symbol shared intrinsic, like the repaired Function or Date, that shares the global prototype of Symbol, disables the shared prototype constructor, and only includes the symbols that SES will permit in shared compartments.

[erights]

Clarification: The reason why lockdown will fail is because these well-known-symbol properties are non-configurable. Otherwise our whitelist mechanism would safety remove them.