fix: match Transformers tojson in chat template rendering

[CISC]

Updates this PR to only carry the remaining chat-template compatibility gap against current main:

• Override Jinja's tojson filter to match Transformers behavior (ensure_ascii=False by default and no HTML escaping).
• Keep the existing generation-tag and loopcontrols extensions intact.
• Add the matching changelog entry.

[CISC]

Since the merging of a similar patch to transformers and the formalizing of tools (see references in #1336) there are starting to pop up a lot more models using tojson in their chat templates.

[CISC]

@abetlen Llama 3.1 is the latest model to use tojson, would be nice to have matching behaviour as transformers.

[CISC]

@abetlen Even more transformers changes incoming, see updated OP.

[CISC]

@abetlen It would be really nice to have this merged soon, it's starting to cause issues with quite a few templates not to have this in place.

Additionally this is a requirement for implementing inverse templates (which I'd like to do, as soon as it's merged in transformers, since it will be super useful for universal function calling and parsing).

[serhii-nakon]

Hello I support to merge it. I have issues with Mistral models (devstral too)

[CISC]

@abetlen I see strftime_now support was finally added, unfortunately that is not enough, PTAL.