Maestro: consider adding a preview function for symbol definitions

[jbirch]

This is probably a bit of a stretch, but it would be awesome if there was some way to preview an XML symbol definition by creating a simple temporary feature source in the session repository and then stylizing it.

I would see this either evaluating the symbol definition to see what Usages it supports (point, line, area), or prompting the user for this information.

Ideally, the features generated for preview would include both overlapping and disjoint points, lines, and polygons.

If this is feasible and there's anything I can do to support this (generate WKT for the features, create layer definition templates to reference temporary styles, etc) please let me know.

[jng]

Without knowing much about symbol definitions, I guess the simplest way to do this is to have a set of "pre-baked" SDF files that each contain lines, points, polygons and various permutations thereof.

Then based on the particular geometry types detected in the symbol definition, we load in the matching pre-baked SDF file into a session repository and generate a preview layer definition off of this SDF file.

[jng]

The best way to get started on this is if I you can attach an SDF file containing the ideal previewable set of features, and any layer templates. Even if I haven't implemented specialized editor support, these resource types can still be previewed via the Generic XML editor.

[jng]

Fixed with the implementation of #1875