Forward createValueFromJsonUtf8 in RuntimeDecorator

[lavenzg]

Summary:
RuntimeDecorator doesn't forward createValueFromJsonUtf8 to the plain runtime, so decorated runtimes use the JSON.parse-based default from jsi.cpp instead of the plain runtime's parser. For Hermes that means makeThreadSafeHermesRuntime and anything built on WithRuntimeDecorator never reach the native parser from a3f615cec.

I think this was missed rather than chosen. WithRuntimeDecorator already overrides it (added in c2a0da2ae as Around plus RD::createValueFromJsonUtf8), which only makes sense if RuntimeDecorator forwards it. Today that RD:: call lands in the default, so it takes one Around plus several nested ones for global, getProperty, createStringFromUtf8 and call. It's also observable: on a thread-safe runtime, after JSON.parse = () => 'hijacked', Value::createFromJsonUtf8 returns 'hijacked', and after delete globalThis.JSON it throws. A plain HermesRuntime parses normally in both cases.

TracingRuntime relies on the current behavior. JSON parsing only shows up in traces because the default splits into traced global/getProperty/call calls. Forwarding alone would hand back a value from the plain runtime with no def, and replay would hit the "has no def" assert in useObjectID. So TracingRuntime now overrides createValueFromJsonUtf8 and calls jsi::Runtime::createValueFromJsonUtf8 explicitly. That runs the same code as before, so traces are unchanged and there's no new record type. If you'd prefer a dedicated SynthTrace record I can do that instead.

A side effect: decorators that watched JSON parsing through global/getProperty/call now need to override createValueFromJsonUtf8, like every other forwarded method. For example, TimedRuntime no longer counts JSON parsing under its call timer. The other methods decorators don't forward yet are the createError* family (facebook/hermes#2203) and String::length (facebook/hermes#2205). React Native's decorator.h has the same gap.

X-link: facebook/hermes#2206

Differential Revision: D124177263

Pulled By: lavenzg

[meta-codesync]

@lavenzg has exported this pull request. If you are a Meta employee, you can view the originating Diff in D124177263.