[Records, dart2js] Optimizations for records

[rakudrama]

This is an ad-hoc list of optimizations that will improve dart2js code quality around records

• Load elimination of literal arrays. Will help to achieve scalar replacement of large records.
• Load elimination (constant folding) of shape property from prototype. Will help with some inlined versions of == and .hashCode.
• Eager initialization of static variables with sufficiently simple record value.

[lin72h]

JS's native Record and Tuple proposal is approaching Stage3, Any thought on the future integration of dart's record and js's record? I think this could be a killer feature.

[bernaferrari]

I'm not from the team, but usually the response to these things is "let's wait until it is stable". It might take years. Similarly to the type in JS that everybody thought would be approved and is still in the limbo.