Globalization API matchers

// Create LocaleList object with well formed list of locales, and save
// languageMatcher for later.
var locales = new LocaleList([...], languageMatcher);

// Create DateTimeFormat object.
// Use localeMatcher function to match available locales to |locales|. It would
// also be used for supportedLocalesOf method call.
// Use dateMatcher function to match options to available pattern.
var dtf = new DateTimeFormat(locales, options, dateMatcher);

// Both localeMatcher and dateMatcher are optional.
// If they are not specified we use default implementation.
// One of the languageMatcher functions can be 'bcp47' matcher.
// Implementations can implement them as native or JS code.
// Users of the library could implement their own.

/*
 * Other way would be to define matchers in global scope:
 */

Globalization.languageMatcher = function() {...};
Globalization.dateTimeMatcher = function() {...};

// I don't think there are any issues with this approach. Already constructed objects would have already resolved the data.
// New object would use new matchers (in case one changed the matchers during the lifetime of given context).