Merge allowList and denyList settings together now that they're objects

[DonJayamanne]

Testing #253103

It feels weird to have a setting such as allowList and denyList and then yet be able to toggle the values of each in the respective lists,

Initially i thought that in allow list if the value was false, then its denied, but thats not true.
I'm thinking of search.exclude if true its excluded else its not. Hence applied the same rationale here.
& assumed that the second list was purely for overriding the allow list.

Could we have a drop down Allow/Deny in each value and consider merging the lists?

[Tyriar]

There are 3 states though:

• Allow - Allow this command, provided it's not denied
• Undefined - Don't consider it
• Deny - Never allow this command, even if it's also allowed

But I like the idea, I'll think about whether we need it to support boolean | null for merging across scopes.

[Tyriar]

This is too large of a change for this late in the release. Since it's experimental and the setting name will change (#253314), let's do this next month. This is what I'm thinking:

"chat.agent.terminal.autoApprove": {
  "echo": "allow",
  "rm": "deny",
  "wget": null // remove entries from higher scopes
}