feat(hugo): replace deprecated language APIs for Hugo v0.158+ compatibility

Replace site.LanguageCode → site.Language.Locale and
.Language.LanguageCode → .Language.Locale in module layouts,
and languageCode → locale in all template language configs.

modules/slides/layouts/slides/baseof.html

@@ -4,7 +4,7 @@
 */}}
 
 <!doctype html>
-{{- $language_code := site.LanguageCode | default "en-us" -}}
+{{- $language_code := site.Language.Locale | default "en-us" -}}
 <html lang="{{$language_code}}" {{ if in hugo.Data.i18n.rtl.rtl $language_code }}dir="rtl"{{else}}dir="ltr"{{end}}
       data-wc-theme-default="{{ (lower site.Params.hugoblox.theme.mode) | default "system" }}"
       data-hbb-relurl="{{ "" | relURL }}">

modules/slides/layouts/slides/baseof.present.html

@@ -21,7 +21,7 @@
 */}}
 
 <!doctype html>
-{{- $language_code := site.LanguageCode | default "en-us" -}}
+{{- $language_code := site.Language.Locale | default "en-us" -}}
 <html lang="{{$language_code}}" {{ if in hugo.Data.i18n.rtl.rtl $language_code }}dir="rtl"{{else}}dir="ltr"{{end}}>
 <head>