[Records] Improve dart2js global type analysis

[rakudrama]

The initial implementation of records in dart2js (#49718) has overly conservative inference results.
This leads to dispatch overhead (e.g. getInterceptor vs array access).

This task is to improve the analysis.

• Perform inference on record fields
  • Inference should have similar precision for each field of a returned record to what it does for returning a non-record value
  • The result of a dynamic getter of a field name should include fields with that name
• Trace records from constants and literals to see if they would benefit from specialization

TODO(50701) is used to mark some the the locations that need improvement.