Investigate global policy support

[joaomoreno]

Enabling global policy support will help system admins to configure VS Code on their networks.

One idea is to allow VS Code settings to opt-in to become policies. If set, a setting's policy value will overwrite any setting source value, whether that's user, workspace, memory or remote.

In progress:

• Update ConfigurationRegistry to support settings opting in to becoming policies @joaomoreno
• Generate Windows Group Policy definition files from static analysis #148941
• Create PolicyService and use it in ConfigurationService #148943
• Surface policy values in settings editor #148944

Future:

• Support macOS Configuration Profiles as a policy backend #148942
• Support JSON file as a policy backend on Linux #148945

References:

• https://github.com/mozilla/policy-templates
• https://docs.microsoft.com/en-us/previous-versions/windows/desktop/policy/implementing-registry-based-policy
• https://docs.microsoft.com/en-us/windows/client-management/mdm/understanding-admx-backed-policies

cc @sana-ajani @sandy081

[sandy081]

Related: #27972