This CL makes the ctor public and externally usable by changing the
camera id argument from an int to a String.
The main purpose with this change is to get rid of the
CameraEnumerationAndroid.setEnumerator() hack. If an external app wants
to have a custom format enumeration, they can just override
getSupportedFormats() instead.
BUG=webrtc:5519
Review-Url: https://codereview.webrtc.org/2012193003
Cr-Commit-Position: refs/heads/master@{#12945}