Posted by scrubber here, translated by Oleg.
Here is my present for you, Google camera 5.1.018.
Portrait mode - both rear and front camera.
HDR+ - both rear and front camera.
This is the first time I upload an apk from this developer. He's "scrubber" on 4PDA. As always, use these files at your own risk.
Versions like this will crash on some phones. Usually this happens because a certain feature is not supported by your phone. For example, the OP3/3T doesn't support (yet?) HDR+ for the front camera and the app will crash. If your phone support all features, then there's a chance you will have a stable and very complete Google Camera.
Oleg noticed the photo metadata shows the maker as "Huawei". This means that "scrubber" used "Nexus 6P" for the config (crisp images, but more noisy than one of the Pixel settings).