Implemented QSV encode

Major updates on AVQt::EncoderQSV:
 - Locks on a source as soon it gets initialized and unlocks after cleanup to prevent issues with multiple frame formats and HW contexts
 - Initializes and cleans up packet sinks on registration/removal if it is running
 - Stores and passes through framerate, because QSV doesn't support VFR, use VAAPI instead for this feature
 - Supports zero-copy encode when input are QSV HW frames

Minor updates:
  - Added libva to link_libraries in CMake config
  - Player example is using the static library instead of the dynamic one
  - Encoding is now enabled by default in example Player

Issue #8 is not solved by this as it only implements QSV encoding

See merge request sdcieo0330/LibAVQt!9