Update MultiLingual and MultiHost methods/functions

- Deprecate .Site.MultiLingual in favor of hugo.IsMultilingual
- Rename hugo.IsMultiHost to hugo.IsMultihost. Cannot deprecate
  in documentation because they have the same published path, but this
  shouldn't be a problem because hugo.IsMultiHost was introduced in the
  last patch release.

See gohugoio/hugo#12232

content/en/functions/hugo/IsMultihost.md

@@ -5,7 +5,8 @@ categories: []
 keywords: []
 action:
   aliases: []
-  related: []
+  related:
+    - /functions/hugo/IsMultilingual
   returnType: bool
   signatures: [hugo.IsMultihost]
 ---

content/en/functions/hugo/IsMultilingual.md

@@ -0,0 +1,37 @@
+---
+title: hugo.IsMultilingual
+description: Reports whether there are two or more configured languages.
+categories: []
+keywords: []
+action:
+  related:
+    - /functions/hugo/IsMultihost
+  returnType: bool
+  signatures: [hugo.IsMultilingual]
+---
+
+{{< new-in v0.124.0 >}}
+
+Site configuration:
+
+{{< code-toggle file=hugo >}}
+defaultContentLanguage = 'de'
+defaultContentLanguageInSubdir = true
+[languages]
+  [languages.de]
+    languageCode = 'de-DE'
+    languageName = 'Deutsch'
+    title = 'Projekt Dokumentation'
+    weight = 1
+  [languages.en]
+    languageCode = 'en-US'
+    languageName = 'English'
+    title = 'Project Documentation'
+    weight = 2
+{{< /code-toggle >}}
+
+Template:
+
+```go-html-template
+{{ hugo.IsMultilingual }} → true
+```

content/en/methods/site/IsMultiLingual.md

@@ -1,6 +1,6 @@
 ---
 title: IsMultiLingual
-description: Reports whether the site is multilingual.
+description: Reports whether there are two or more configured languages.
 categories: []
 keywords: []
 action:
@@ -9,6 +9,12 @@ action:
   signatures: [SITE.IsMultiLingual]
 ---
 
+{{% deprecated-in 0.124.0 %}}
+Use [`hugo.IsMultilingual`] instead.
+
+[`hugo.IsMultilingual`]: /functions/hugo/ismultilingual/
+{{% /deprecated-in %}}
+
 Site configuration:
 
 {{< code-toggle file=hugo >}}