Export the mockgen API as a library for use by other projects in generating mock codes.

[sysulq]

I have a project here, github.com/hnlq715/struct2interface, which converts structs into interfaces. I'm looking to take it a step further—being able to automatically generate mock structures based on interfaces. Currently, I can only generate them directly using mockgen binary. It would be perfect if it could support a library format.

Thanks in advance~