fix(web): make date format functions globally accessible

Remove const declarations from exported functions (getDateFormat,
getMediumDateFormat, etc.) to make them available on the global scope.
Replace comma operators with semicolons in minified version to prevent
functions from being block-scoped.

This fixes the 'dart.global.getDateFormat is not a function' error
when calling SystemDateTimeFormat().getDatePattern() on Flutter Web.

Closes: #31

Author: Nikoro

web/system_date_time_format.js

@@ -18,8 +18,8 @@ const getDateTimeFormatPattern = (options) => {
     .join("");
 };
 
-const getDateFormat = () => getDateTimeFormatPattern({ dateStyle: "short" });
-const getMediumDateFormat = () => getDateTimeFormatPattern({ dateStyle: "medium" });
-const getLongDateFormat = () => getDateTimeFormatPattern({ dateStyle: "long" });
-const getFullDateFormat = () => getDateTimeFormatPattern({ dateStyle: "full" });
-const getTimeFormat = () => getDateTimeFormatPattern({ timeStyle: "short" });
+getDateFormat = () => getDateTimeFormatPattern({ dateStyle: "short" });
+getMediumDateFormat = () => getDateTimeFormatPattern({ dateStyle: "medium" });
+getLongDateFormat = () => getDateTimeFormatPattern({ dateStyle: "long" });
+getFullDateFormat = () => getDateTimeFormatPattern({ dateStyle: "full" });
+getTimeFormat = () => getDateTimeFormatPattern({ timeStyle: "short" });