Implement subtitle handling for TTML subtitles

package-lock.json

package.json

src/assets/fonts/subtitles.css

src/global.d.ts

src/index.tsx

src/routes/player/Player.tsx

src/routes/player/subtitles/TtmlHelper.ts

src/routes/player/subtitles/TtmlRenderer.tsx

src/routes/player/video/DashVideoElement.tsx

src/routes/player/video/RawVideoElement.tsx

src/routes/player/video/VideoElement.tsx

src/util/ttml/doc.js

src/util/ttml/html.js

src/util/ttml/isd.js

src/util/ttml/ismc.ts

src/util/ttml/names.js

src/util/ttml/styles.js

src/util/ttml/utils.js