Remove synthetic principals hack in Resolver

#5119 is introducing external principals, and is also introducing a temporary "hack" in the Resolver: synthetic principals and principal roles.

Synthetic principal and roles are a temporary workaround for external principals, until external authorizers change their implementation of `PolarisAuthorizer.resolveAuthorizationInputs()` to avoid calling `PolarisResolutionManifest.resolveAll()`, and instead only resolve the securables that are actually needed for authorization, cf. `PolarisResolutionManifest.resolveSelections()`.

Start by reading issue #5119 and the Resolver code, then trace PolarisAuthorizer.resolveAuthorizationInputs() and PolarisResolutionManifest.resolveAll() versus resolveSelections(). Confirm how synthetic principals and principal roles are used; done means the temporary workaround is removed without breaking authorization for external principals.

Written by the indexing model from the issue text.