Feature: Tap to Focus

[alistairsykes]

#11

This is a complex feature to implement. Rough steps for requesting focus on camera2:

• Cancel the previous repeating request (used for previous and image analysis)
• Cancel any previous focus requests (have to call capture to do this)
• Create a focus request. This is essentially a single capture request with some specific settings for the area of the sensor you want to focus on.
• Restart the repeating request with the focus area also set

Once you complete these steps the camera will actual stay focused on that area of the sensor. Therefore it makes sense to clear that focus a period of time later (5000 millis, copied from camerax. Added ability to set to make it flexible). And resume the automatic focus.

We setup a touch listener within BarcodeView which then calls down eventually into the Camera2Source.

I will update the wiki as needed once this PR is in.

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This change is 

[alistairsykes]

I have written a wiki update for this, which I can send you @NickHolcombe before I publish if you like?

[robertredwood]

I'm not able to see any obvious issues with this approach. Thanks for providing such great supporting information alongside what is definitely a complex feature. LGTM.

Reviewed 13 of 13 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @alistairsykes)