Add `mistral-v1`, `mistral-v3`, `mistral-v3-tekken` and `mistral-v7` chat template types (#10572)

* Templates: `mistral-v1`, `mistral-v2`, `mistral-v3`, `mistral-v3-tekken`

* Changed system message logic and added tests for all 4

* Invalid `system_message` instead of `content` fixed

* Removed tab-indented lines

* Added template code and test for `mistral-v7`

* Added all tests. Fixed bug with `tmpl == "llama2"` test.

* Replaced tabs with spaces.

* Removed `'mistral-v2'` option as no (open) models ever used it

* Removed all references to 'v2' template from comments

* Update llama.cpp

Fixed `trim_assistant_message` bug