Turn into sub-issues as needed.

• Python support
  • Extensions
  • Unit test (constructors, serialization)
  • Doc example
• Rust support
  • Extensions
  • Unit test (constructors, rust-to-rust roundtrip)
  • Doc example
• C++ support
  • Extensions
  • Unit test (constructors, serialization)
  • Doc example
• Cross-language roundtrip test
• Remove old components
  • Clean up re_components
  • Port viewer to use new types and queries