Fix scrubbing mode stall that can occur when seeking to 'end of stream'

A prominent feature of scrubbing mode is the blocking of all interrupting seek requests when actively processing a seek. After the current seek is completed, `ExoPlayerImplInternal` will process any pending seek request. However, if a seek results in processing an 'end-of-stream' buffer then `ExoPlayerImplInternal` will be blocked until scrubbing mode is disabled.

The solution is that if a `seekIsPendingWhileScrubbing` but relevant renderers have ended, then `ExoPlayerImplInternal` should mark the active seek as "completed".

PiperOrigin-RevId: 945108967
(cherry picked from commit 829647bba235f48fef31be6a6a23ca8204232702)