Variant to string convertion should use CurrToStr for varCurrency

Summary

Now,

VariantVar := ReallyLargeCurrencyVar;
StrVar := VariantVar; // here compiler use FloatToStr to convert currency to string

But due to the implementation of FloatToStr, it outputs unexpected result for large currency (822337203685477.5807 -> "822337203685478")

System Information

• Operating system: Linux (ubuntu)
• Processor architecture: x86-64
• Compiler version: trunk (299c90b9)
• Device: Computer

Steps to reproduce

var
  C: Currency;
  V: Variant;
  S: string;
begin
  C := 822337203685477.5807;
  V := C;
  S := V;
  WriteLn(S); // Expected 822337203685477.5807, actual 822337203685478
end;