Add cdlatex support in latex: +cdlatex

cdlatex has 4 main functionalities:
+ Math and environments snippets: I've disabled these in favor of
  yasnippet when using :editor snippets by just unbinding the TAB in
  cdlatex's keymap
+ Auto insertion of closing delimiters: disabled in favor of smartparens
+ Fast insertion for some macros: `a becomes \alpha. Kept as-is
+ Fast accent insertion: a'~ becomes \tilde{a}. Kept as-is

I also updated the docs, and added a section explaining how to re-enable
cdlatex's snippets despite having yasnippet.

modules/lang/latex/packages.el

@@ -10,6 +10,9 @@
 (when (featurep! +latexmk)
   (package! auctex-latexmk :pin "4d35352265"))
 
+(when (featurep! +cdlatex)
+  (package! cdlatex :pin "b7af5a9884"))
+
 ;; Features according to other user selected options
 
 (when (featurep! :completion company)