[Feature Request]: Change ProfileId defaulting to be an invalid profile

[BenHenning]

Is your feature request related to a problem? Please describe.

Currently, a default (unspecified) proto3 proto message will default its integers to 0. In the case of ProfileId, this means it defaults to an internal profile ID of 0.

An oversight when designing the profile management system is that the admin profile (first profile created on the device) is also initialized to 0, despite the default logged out ID being -1. This creates a potentially buggy inconsistency where code may assume a default, uninitialized ProfileId corresponds to an invalid profile when, in reality, it probably corresponds to the admin profile.

Describe the solution you'd like

ProfileId needs to be refactored to have a proper uninitialized state, which can probably be best done by introduce a logged out value:

message ProfileId {
  oneof type {
    int32 logged_in_internal_profile_id = 1;
    bool logged_out = 2; // Can be true or false; presence is sufficient.
  }
}

This should be binary compatible with the existing ProfileId, but it changes the semantics of default ProfileId to be an unspecified type, rather than a type that's logged in.

However, this requires substantial changes still throughout the codebase, namely:

• All assumptions (including in ProfileManagementController) that '-1' means 'logged out' should be changed to use an actual logged-out state ProfileId.
• All cases where internalProfileId is extracted from a ProfileId need to be checked to ensure that ProfileId's type is the correct logged-in case.

Describe alternatives you've considered

Haven't considered alternatives, but there are likely many approaches to this problem.

Additional context

Came up during review of #5248 but I was aware of it prior to that PR since it's existed as an issue since the introduction of profiles support.