Add EcDsa::generate_key for convenience am: 0987e270cf am: 170113645b am: ba53954d48

Original change: https://android-review.googlesource.com/c/platform/system/authgraph/+/2901989

Change-Id: Ic8cd02599d246ed412b0ec9c851daef2899f8fe2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>