fix loading of language name from kernel_info

language is langinfo.name, not langinfo.language

fixes highlighting for IJulia kernels
move language name, version into language_info

in kernel_info_reply

adds adaptation of language info to msgspec adapter
add language_info to nbformat doc and spec
update kernel_info_reply test
validate codemirror_mode
Merge pull request #6945 from minrk/kernel-info-lang

fix loading of language name from kernel_info