demux: subtitle: optimize to avoid strcat, strlen, allocation when appending

changed milestone to %4.0

added Component::Demuxers: Subtitles label

added MRStatus::Reviewable label

added MRStatus::InReview label and removed MRStatus::Reviewable label

resolved all threads

added MRStatus::Acceptable label and removed MRStatus::InReview label

added MRStatus::Accepted label and removed MRStatus::Acceptable label

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This MergeRequest has been Accepted! Congratulations.

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added 41 commits

• 25a077d7...46cacbe0 - 36 commits from branch videolan:master
• 3f110c95 - demux: subtitle: only allocate internal psz_text when needed
• e8f7ac27 - demux: subtitle: avoid using strcat when we know the string sizes
• 1e03b716 - demux: subtitle: keep the size of the concatenated string
• de7e5074 - demux: subtitle: avoid allocating a dummy string
• 1f9b8484 - demux: subtitle: only set the string terminator on loop exit

Compare with previous version

added Status::BackportCandidate label

enabled an automatic merge when all merge checks for 1f9b8484 pass

added MRStatus::NotCompliant label and removed MRStatus::Accepted label

added MRStatus::Accepted label and removed MRStatus::NotCompliant label

merged

mentioned in merge request !7012 (merged)