This PR includes commits from #16234, I will rebase once that PR gets merged.

Per spec: InitializeInstanceElements

The method initializers should run before any fields are defined.

In the REPL example,

let initCalled;

function dec(value, context) {
  context.addInitializer(() => initCalled = true);
}

class C {
  @dec m() {}
  p = initCalled;
}

console.log((new C).p)

When the property p is defined, the initCalled should be true. Previously we inject the protoInit calls in the first decorated field, in this PR we move the field initializer injection out of the hasDecorators branch.