This commit adds new option to "Worker" Web API that allows to
configure permissions.
New "Worker.deno.permissions" option can be used to define limited
permissions to the worker thread by either:
- inherit set of parent thread permissions
- use limited subset of parent thread permissions
- revoke all permissions (full sandbox)
In order to achieve this functionality "CliModuleLoader"
was modified to accept "initial permissions", which are used
for top module loading (ie. uses parent thread permission set
to load top level module of a worker).
Fixes panic occurring in worker when "self.close()" is called
at the top level, ie. worker shuts down while
module evaluation promise hasn't yet resolved.
