Update DXF Export (app and processing) documentation

[gacarrillor]

• Fix Add option 'Use only selected features' to DXF export (Request in QGIS) #8961
• Processing:
  • Adjust default value for MTEXT parameter.
  • Add missing parameter EXTENT.
  • Add missing parameter MAP_THEME (also added to possible processing parameter values).

[gacarrillor]

@DelazJ, should these icons reflect the default value for each checkbox?

I'm asking because if that's the case, I could update them in this PR.

[DelazJ]

should these icons reflect the default value for each checkbox?

@gacarrillor Yes, that was the idea. Thanks for fixing.

Do you also plan to clarify what the layer title refers to?

[DelazJ]

I don't think this is necessary. I see the list has unnecessarily grown... The initial intent was to list available specific widgets and assign to parameters the one they used in the GUI.
Specifically, map themes are text string in a combobox, so I would just go with enumeration but I see there is already a "maptheme" type.
I will try to revisit this in upcoming weeks. Any idea/feedback for clarification will be more than welcome in the meantime... (I must admit I'm myself confused on how these are used throughout the docs)

[gacarrillor]

Right, map extent and map theme have already their own processing widgets, so IMHO when users/devs look at the docs (e.g., to replicate the widget in a custom processing algorithm), it'd be great if we could point them at the more specific widget, i.e., instead of pointing them to an enumeration, we could let them know they can/should use the more specific map theme widget.

[gacarrillor]

should these icons reflect the default value for each checkbox?

@gacarrillor Yes, that was the idea. Thanks for fixing.

I'll do that in this PR.

Do you also plan to clarify what the layer title refers to?

Sure! I started by asking for some agreement here and now that the scenario is clearer we could explain a little bit both the title provenance.

[DelazJ]

Yes! sorry for the silence, holidays... and I noticed that things were sorted out in the meantime.

[gacarrillor]

should these icons reflect the default value for each checkbox?

@gacarrillor Yes, that was the idea. Thanks for fixing.

Do you also plan to clarify what the layer title refers to?

Done!
Note this is not the only PR for which I'll need to touch DXF export docs. If that's fine for you, we could merge this one to do incremental changes via PRs. Otherwise, all upcoming changes (e.g., this, this and this ) would need to land in this PR.

Yes! sorry for the silence, holidays... and I noticed that things were sorted out in the meantime.

No worries, that was my first guess! :)