fix(data): correct XML closing tag insertion

`nxml-slash-auto-complete-flag` inserts the rest of the closing tag when
`</` is inserted, but smartparens also defines `(sp-local-pair "<" ">")`
for `sp--html-modes`, so two `>` are inserted for closing tags. Apply
the upstream developer’s suggested fix.

Fix: https://github.com/doomemacs/doomemacs/issues/6331
Ref: https://github.com/Fuco1/smartparens/issues/397

modules/lang/data/config.el

@@ -7,6 +7,9 @@
   :config
   (setq nxml-slash-auto-complete-flag t
         nxml-auto-insert-xml-declaration-flag t)
+  ;; https://github.com/Fuco1/smartparens/issues/397#issuecomment-501059014
+  (after! smartparens
+    (sp-local-pair 'nxml-mode "<" ">" :post-handlers '(("[d1]" "/"))))
   (set-company-backend! 'nxml-mode '(company-nxml company-yasnippet))
   (setq-hook! 'nxml-mode-hook tab-width nxml-child-indent)
   (set-formatter! 'xmllint '("xmllint" "--format" "-") :modes '(nxml-mode)))