OgrFileExport: Exclude objects with hidden or helper symbols

[dl3sdo]

The geospatial vector export shall not export objects with hidden or helper symbols.
However, if the "Create a layer for each symbol" setting in the GDAL/OGR configuration was not set then objects with hidden or helper symbols would not be excluded.

[dl3sdo]

ChatGPT (and me) propose a better commit message:
Previously, objects with hidden or helper symbols were exported if the “Create a layer for each symbol” option in the GDAL/OGR configuration was disabled.
This change ensures that such objects are always excluded, independent of the configuration.

[dg0yt]

I prefer concise commit messages, and so far I prefer to not be bothered with reviewing LLM output.

[dg0yt]

Hm, noticing a mismatch between function name and function result 🤔

The original design was:
These functions really test only symbol type. (ìs_point_symbol).
Helper symbols and hidden symbols are excluded by creating a curated list of symbols first (auto symbols = symbolsForExport();). This list is also useful for populating the style table.

But the "per-symbol layers" export doesn't use the curated list when populating the layers.

[dl3sdo]

@dg0yt: thank you for your feedback. That led me to reconsider the current solution, and I believe I’ve found a more elegant approach.

[dl3sdo]

Now merging everything in an unified approach.