"IMSC and other standards" should mention newer TTML-IMSC

### MDN URL

https://developer.mozilla.org/en-US/docs/Related/IMSC/IMSC_and_other_standards

### What specific section or headline is this issue about?

_No response_

### What information was incorrect, unhelpful, or incomplete?

As mentioned in https://github.com/mdn/content/pull/39861#discussion_r2136643452, we should document TTML 1.2 and 1.3 as well, and even TTML 2. I'm not sure how their support should be documented, or if old versions are relevant at all, but we should seek to modernize this information in any case. Eventually, the goal is to remove the links to https://www.w3.org/TR/ttml-imsc1.0.1/ and https://www.w3.org/TR/ttml-imsc1.1/, which are the only remaining w3.org/TR/ links.

### What did you expect to see?

New standards to be documented and presented as canonical.

### Do you have any supporting links, references, or citations?

_No response_

### Do you have anything more you want to share?

_No response_

### MDN metadata

Page report details

* Folder: `en-us/related/imsc/imsc_and_other_standards`
* MDN URL: https://developer.mozilla.org/en-US/docs/Related/IMSC/IMSC_and_other_standards
* GitHub URL: https://github.com/mdn/content/blob/main/files/en-us/related/imsc/imsc_and_other_standards/index.md
* Last commit: https://github.com/mdn/content/commit/636b90011532e3fd2cf9333aaf1754fdc8de7938
* Document last modified: 2025-06-10T14:48:09.000Z