Add subtitles during video upload

[swissspidy]

See #227

Just a POC for now. Can't really use it as the video block doesn't know about the tracks in its onChange callback.

Thus also no tests.

[github-actions]

Size Change: +302 B (0%)

Total Size: 7.31 MB

Filename	Size	Change
build/media-experiments.js	81.3 kB	+154 B (+0.19%)
build/view-upload-request.js	19.1 kB	+148 B (+0.78%)

ℹ️ View Unchanged

Filename	Size
build/100.js	89.6 kB
build/699.js	2.35 MB
build/ai.worker.js	178 kB
build/blurhash.worker.js	3.23 kB
build/canvas.worker.js	2.79 kB
build/chunk-ffmpeg.js	5.92 kB
build/chunk-selfie-segmentation.js	16.3 kB
build/dominant-color.worker.js	4.45 kB
build/ffmpeg.js	1.09 kB
build/heif.worker.js	450 kB
build/media-experiments-blocks-rtl.css	318 B
build/media-experiments-blocks.css	318 B
build/media-experiments-rtl.css	1.03 kB
build/media-experiments.css	1.03 kB
build/pdf.js	579 B
build/subtitles.js	850 B
build/view-upload-request-view-rtl.css	697 B
build/view-upload-request-view.css	699 B
build/vips-heif.********.wasm	1.27 MB
build/vips-jxl.********.wasm	800 kB
build/vips.********.wasm	2 MB
build/vips.worker.js	37.9 kB

_{compressed-size-action}