dillon1000/react

[Flight/Fizz] Use Constructors for Large Request/Response Objects in Flight/Fizz (#29858)

We know from Fiber that inline objects with more than 16 properties in
V8 turn into dictionaries instead of optimized objects. The trick is to
use a constructor instead of an inline object literal. I don't actually
know if that's still the case or not. I haven't benchmarked/tested the
output. Better safe than sorry.

It's unfortunate that this can have a negative effect for Hermes and JSC
but it's not as bad as it is for V8 because they don't deopt into
dictionaries. The time to construct these objects isn't a concern - the
time to access them frequently is.

We have to beware the Task objects in Fizz. Those are currently on 16
fields exactly so we shouldn't add anymore ideally.

We should ideally have a lint rule against object literals with more
than 16 fields on them. It might not help since sometimes the fields are
conditional.