0024326: Get rid of confusing extension line

0024326: Get rid of confusing extension line

1) Removed confusing part of labeled extension for 3d text.
2) Removed unused "TextOffset" property of AIS_Dimension class, revised function of "ExtensionSize" property.
3) Added options to specify automatic or user-defined arrow orientation and value label positioning to dimension aspect enumerations.
4) Use proper naming: Prs3d_DimensionTextVerticalPosition, Prs3d_DimensionTextHorizontalPosition instead of Prs3d_HorizontalTextAlignment, Prs3d_VerticalTextAlignment.
Correction of label length computing method.