Rename some methods in DataParams

[mdbs99]

Rename these methods to be more consistent with others.

From:

    function SaveAs(aDest: TParams): IDataParams;
    function AsString(const SeparatorChar: string): string; overload;
    function AsString: string; overload;

To:

    function ToParams(aDest: TParams): IDataParams;
    function ToString(const aSeparator: string): string; overload;
    function ToString: string; overload;

[mdbs99]

More correct is:

    function AsRawUTF8(const aSeparator: RawUTF8): RawUTF8; overload;
    function AsRawUTF8: RawUTF8; overload;
    function ToParams(aDest: TParams): IDataParams;