(This is a merge of http://go/wvgerrit/29282)
The Android API has long mandated that plugins respond to queries for a
version number, but we'd never hooked it up to the CDM's actual version
number until now.
Bug: 36867286
Test: libwvdrmdrmplugin_test
Test: libwvdrmdrmplugin_hidl_test
Change-Id: I952de4943f8e78b44d526bee66c54d31e9fe5ff1