This fixes seeking within sample grabber by matching Windows functionality. -- v5: mf: Request new sample before processing markers. mf: Remove no longer used sample_count and samples array. mf: Ensure we always have four requests outstanding/satisfied. mf: Always queue a sample unless stopped. mf: Keep count of samples queued. mf: Make flushing on sample grabber largely a no-op. mf/tests: Test sample grabber pause and resume. mf/tests: Check contents of sample collection. mf/tests: Test seek with sample grabber whilst ignoring clock. mf/tests: Test samplegrabber flush then seek. mf/tests: Check StreamSinkMarker event. mf/tests: Test sample grabber {Set,Cancel}Timer. mf/tests: Add test for sample grabber seek. https://gitlab.winehq.org/wine/wine/-/merge_requests/9489