Without this, Playwright's CDP feature leaves unreachable
targets (namely OOPIFs).
This change allows for more advanced experimentation in user-land
without relying on out-of-band CDP connections and clients.
Now you can, for example, call `DOM.getDocument` on the
page OR main frame, observe there is an iframe node with
no `contentDocument` (i.e. OOPIF), make note of the referenced
`frameId`, and then iterate of page.frames() calling `Target.getInfo`
on each to link the Playwright Frame with the CDP `frameId` and
then recurse.
Relates #8113
101662765c
