Add LaTeX and BibTeX modes with tested highlighting and indentation

[tani]

Caution

This is AI generated code

I create a latex-mode and bibtex-mode related to #2066 .

[vindarel]

Hi, looks impressive. Did you use it for a few days?

Do all functions and variables that live in the lem-bibtex/latex-mode packages need a "bibtex-" prefix? (mostly thinking about the utility functions)

(defun bibtex-line-blank-p (line)
(uiop:emptyp (string-trim '(#\space #\tab) line)))

and latex-line-blank-p

=> what about str:blankp ? This avoids re-implementing a utility function.

(defun get-point-at-line-char …]

is duplicated between bibtex an latex tests.

(defun attribute-at …]

also

(defun calc-indent-at-line …)

too

[tani]

Thank you! Please note that this is currently a draft Pull Request. I’ve just finished the initial script and haven't put it into active use yet, so it isn't quite ready for a formal review. I’d appreciate one to two weeks to polish the code quality. Thanks for your patience!