initializeDateSymbols function
Initialize the symbols dictionary. This should be passed a function that creates and returns the symbol data. We take a function so that if initializing the data is an expensive operation it need only be done once, no matter how many times this method is called.
Implementation
void initializeDateSymbols(Function symbols) {
if (dateTimeSymbols is UninitializedLocaleData<dynamic>) {
dateTimeSymbols = symbols();
}
}