JSG Completion: add interim jsg::Lock::v8Set and jsg::Lock::v8Get

[jasnell]

Help to eliminate v8 specific boilerplate when getting/setting values on v8::Object instances. This should be considered transitional. It helps to eliminate a number of direct uses of v8::Isolate and other v8 specific APIs but does not completely hide the v8 semantics.

For example,

  jsg::check(bound->Set(js.v8Context(), jsg::v8StrIntern(js.v8Isolate, "foo"_kj), handler.wrap(js, JSG_THIS)));

  // becomes

  js.v8Set(bound, "asyncResource"_kj, handler.wrap(js, JSG_THIS));

[kentonv]

Is the idea that eventually we'll have a wrapper for v8::Local<v8::Object> that has get() and set() methods?

I guess v8Set() and v8Get() have the funny-looking v8 prefix because they operate on v8::Local rather than a JSG wrapper type?

[jasnell]

Is the idea that eventually we'll have a wrapper for v8::Local<v8::Object> ...

I think so but still thinking through it.

I guess v8Set() and v8Get() have the funny-looking v8 prefix ...

Yep, that's exactly it.

[kentonv]

Approved assuming v8Set can be changed to return void.