[S] Change in flashrom[master]: libflashrom: Allow getting the progress_state from the flashctx

[Nico Huber (Code Review)]

Attention is currently required from: Felix Singer, Richard Hughes, Edward O'Callaghan, Angel Pons, Daniel Campello, Anastasia Klimchuk.

Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/64663 )

Change subject: libflashrom: Allow getting the progress_state from the flashctx
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Patch Set 2:

(1 comment)

File include/libflashrom.h:

https://review.coreboot.org/c/flashrom/+/64663/comment/baf5b056_0183b674 
PS2, Line 85: typedef void(flashrom_progress_callback)(struct flashrom_flashctx *flashctx);
> Nico, if we understand you correctly, flashctx should be kept internal, and the API should have a di […]

Yes about `flashctx`. But with `user_data` I mean the generic (opaque) object passed
around as void pointer. This is a common concept for callback functions. Beside the
function, the API user passes any information that it likes to associate with the
callback function calls. The implementation behind the API, that calls the callback,
has no idea about this data, hence just a void pointer, no struct.

The `flashctx` may or may not be needed by the callback as well. We can either
have it as parameter (which would probably be unused by callback implementations),
or let the API user handle it: they already have it, and can store it in their
`user_data` object if needed, or have things simple if they don't need it.

Quite generally, I think these APIs are best to be discussed with their users
(to reach a reasoable dependency inversion [1]). Looking at [2] for instance,
I see no need for `flashctx`. Other use cases may differ, though.

[1] https://en.wikipedia.org/wiki/Dependency_inversion_principle (not necessarily
worth reading more than the basic idea)
[2] https://github.com/fwupd/fwupd/pull/4675