Move to different entitlements files for parent and child processes

Mozilla started to provide/use different entitlements files for parent and child processes to be able to provide a finer-grained ruleset for the hardening depending on process type:

https://bugzilla.mozilla.org/show_bug.cgi?id=1593071 https://bugzilla.mozilla.org/show_bug.cgi?id=1593072

We should do the same for Tor Browser.

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