HackStudio: Add syntax highlighting for HTML, Shell, and SQL files

.html files were recognised before -- the name was shown on
the statusbar, but it didn't actually enable the syntax highlighting.

This also sneaks a highlighting for JSON using JS highlighting.
It isn't technically correct, but so does TextEditor. :^)

Userland/DevTools/HackStudio/Language.h

@@ -13,9 +13,11 @@ enum class Language {
     Unknown,
     Cpp,
     JavaScript,
+    HTML,
     GML,
     Ini,
     Shell,
+    SQL,
 };
 
 Language language_from_file_extension(const String&);