Top-level CMake targets

[GregoryComer]

🚀 The feature, motivation and pitch

Implement single top-level targets.

Previously discussed in build design review and #12138.

Alternatives

No response

Additional context

No response

RFC (Optional)

No response

[larryliu0820]

Let's make sure we can install these top level libraries

[larryliu0820]

Also 100% we should have top level selective build API

[GregoryComer]

Handling a few small follow-ups and will merge by EOD tomorrow.