[camerax] Standardize the detached versions of wrapped class constructors #126293
Description
Currently, some of the detached versions of the dart wrapped class constructors create a HostApiImpl in their constructor, and some do not
Examples that do not create a HostApiImpl:
Exposure state
Zoom state
Examples that do:
Preview
Image proxy
We should standardize these constructors to either all construct a HostApiImpl corresponding to their class, or to all not create them in the detached constructor.
See this discussion which brought up this issue.