[OpenCV 3] update to v3.4.7

[cenit]

align the portfile to the opencv4 one to ease mainteinance

[vicroms]

We should have separate PRs for both versions, so that improvements on OpenCV 4 don't get delayed because of OpenCV3.

[cenit]

as of now, any touch on opencv4 is not an improvement to the port itself, it is just to ease alignment.

I am trying to uniform ports so that mainteinance can be very easy also on "older" opencv3

[cenit]

Base work should be ready.
@vicroms if you have anyone interested in opencv3, please let them try this update, then it might be ready for merging, having already all the improvements that went into opencv4.
The huge work went into the dependencies, now we are very quick in adopting new releases and if opencv3 can also receive some love then why not :)
(shall I reopen the opencv2 port PR? 🤣 )

[cenit]

I also tried to minimize raw diffs between opencv4 and opencv3 ports. They should look as similar as possible. Any difference should be due to something necessary, otherwise I tried to remove all of them. Naming inside the control file, names of the patches themselves, ...

Fixed vcpkg_check_features() call

[vicroms]

This LGTM, @cenit are there any other pending changes?

[vicroms]

(shall I reopen the opencv2 port PR? 🤣 )

I know you're joking (right? 😅), but I got word from a team that might actually want to use OpenCV 2.4, (luckily they're aware of --overlay-ports) 😟

[cenit]

Nothing pending for now. You can merge

I was joking, yes, but the PR for 2.4 is easy to be reopened... #7849

[cenit]

there was a bug (typo) inside your last commit (FEATURE OPPTIONS with double P) 8bd3aab, which unfortunately i didn't even test so I didn't notice.
The fix is inside #7536