Annotation drawing should be faster when display is dense

[louisewatson]

When there are many annotations displayed, the current drawing time is too slow.

[louisewatson]

Fixed by submission ​http://trac.osgeo.org/mapguide/changeset/3462

The changes made to improve the annotation drawing speed were:

1. When text height is 3 pixels or less a line is drawn instead of the text which would not have been readable. This action is controlled by the value returned by the new SE_Renderer::OptimizeGeometry method. That is, if OptimizeGeometry returns true, then it is OK to perform drawing optimizations. If a renderer does not wish to use optimization, then it needs to override the OptimizeGeometry method and return false.
2. The result of the call to RS_FontEngine::GetTextMetrics is now stored in the

SE_RenderText object so that this data can be reused rather than recalculated when the text is drawn.