multimedia/x264: General overhaul

- Split x264 into two ports: the CLI application (x264), and the library 
  (libx264). This will allow x264 to use lavf and friends from ffmpeg for
  decoding and demuxing while preventing a circular dependency between the
  two: x264 can depend on ffmpeg, but ffmpeg will depend on libx264 rather
  than x264.
- Add the LAVF option to the CLI port, making the dependency on ffmpeg
  optional.
- Update to 0.142.2455.
- Amend fixes to local patches so that they can apply to the new upstream
  files.
- Provide the git revision and other version information to the build
  environment, allowing the CLI binary to display this information (like the
  Windows builds).
- Remove unsupported build options (X11_OUTPUT).
- Ensure that the library and CLI ports each have the appropriate options.
- Add notes for future contributors who wish to update the ports.
- Bump PORTREVISION for all dependent ports.

PR:           187805
DiffRev:      placeholder
Submitted by: Andrew Berg <aberg010@my.hennepintech.edu>
Approved by:  koobs (maintainer, mentor)