buffer: Add more exhaustive test for gst_buffer_foreach_meta() meta removal

Existing test for iterating/removing buffer meta data was insufficient
to detect linked list corruption when removing multiple items, and could
also suffer from such corruption in attempting to count remaining items.
Modified the one test and added several others to exercise multiple
scenarios.

Validates fix for issue #332.
4 jobs for gstbuffer-foreach-fix in 10 minutes and 57 seconds (queued for 9 minutes and 9 seconds)
Status Name Job ID Coverage
  Preparation
passed gst indent #57126

00:01:18

passed manifest #57125

00:00:48

 
  Build
passed build fedora x86_64 #57127

00:05:53

 
  Full Builds
passed build android arm64 api28 #57128

00:02:57