Remove string members in render styles

[waltweltonlair]

The SE_RenderStyle derived structs contain a number of string members (e.g. angleControl, vertexControl), and the rendering code uses string comparison calls to branch based on their values. This all happens inside the rendering loop. A more efficient implementation is to use enumerated types in place of these string members. In the common case (no expressions) the strings are then evaluated only once when the style is evaluated.

[waltweltonlair]

Another benefit to doing this is that schema-specific behavior (such as handling of deprecated and default values) is less spread out.

[waltweltonlair]

Implemented with submission  https://trac.osgeo.org/mapguide/changeset/3102.

[waltweltonlair]

Merged fix into branch stream with submission  https://trac.osgeo.org/mapguide/changeset/3130.