videotimecode: Set the DROP_FRAME flag when parsing timecodes with a ,/; from a string

And also add a test for parsing a few valid and invalid timecodes
6 jobs for video-timecode-fixups in 31 minutes and 40 seconds (queued for 1 second)
Status Job ID Name Coverage
  Preparation
passed #67981
gst indent

00:00:33

passed #67980
manifest

00:00:37

 
  Build
passed #67982
build fedora x86_64

00:04:56

 
  Test
passed #67983
check fedora

00:16:27

 
  Full Builds
passed #67984
build android arm64 api28

00:05:27

passed #67985
build cerbero fedora x86_64

00:09:39