Option to preload heuristically-determined hero image

[twifkak]

This would likely significantly boost the LCP improvement from prefetching. It would provide parity with AMP Packager's preloadimage, though needn't use the same set of heuristics.

I'm not familiar enough with the architecture of webpackager. Does this make more sense as a new Processor, a new HTMLTask, or something else?

[banaag]

I defer to @yuizumi for the definitive response, but from my limited experience working on web packager, this looks like an HTMLTask.

[yuizumi]

@banaag's right ― HTMLTask should be the best option for the given purpose.