Update TPath.Combine to reflect changes from Delphi 12

In Delphi 12 TPath provides following methods now:

class function Combine(const Path1, Path2: string; const ValidateParams: Boolean = True): string; overload; inline; static;
class function Combine(const Path1, Path2, Path3: string; const ValidateParams: Boolean = True): string; overload; static;
class function Combine(const Path1, Path2, Path3, Path4: string; const ValidateParams: Boolean = True): string; overload; static;
class function Combine(const Paths: array of string; const ValidateParams: Boolean = True): string; overload; static;

Source: https://docwiki.embarcadero.com/RADStudio/Athens/en/What%27s_New#Additional_RTL_Improvements