Add initialisation for TFraction in later Delphis

[delphidabbler]

Default initialisation of TFraction leaves it in an invalid state. When declared as a field the state could be that all fields are zero, giving an invalid denominator.

Add initialisation to set numerator to 0 and denominator to 1 where initialisation of records is supported.

[delphidabbler]

Need methods of custom managed records introduced in Delphi 10.4. Use conditional compilation with:

CompilerVersion >= 34.0