DXF Export app functionality not offered by its processing alg and settings not remembered

[gacarrillor]

What is the bug or the crash?

Just to keep track of this, PR #56428 (Create DXF blocks for point symbols with data defined properties) introduced functionality to DXF Export app dialog that is not offered in the corresponding processing algorithm and also added settings that are not remembered (namely, allow data defined symbol blocks and maximum number of blocks).

Steps to reproduce the issue

1. Project --> Import/Export --> Export project to DXF...
2. Export points to DXF using data defined symbol blocks.
3. Close and reopen the dialog. Your recently-used symbol block settings are gone.

Versions

QGIS version	3.37.0-Master	QGIS code revision	066da2e1002
Qt version	5.15.3
Python version	3.10.12
GDAL/OGR version	3.4.1
PROJ version	8.2.1
EPSG Registry database version	v10.041 (2021-12-03)
GEOS version	3.11.1-CAPI-1.17.1
SQLite version	3.37.2
PDAL version	2.3.0
PostgreSQL client version	14.11 (Ubuntu 14.11-0ubuntu0.22.04.1)
SpatiaLite version	5.0.1
QWT version	6.1.4
QScintilla2 version	2.11.6
OS version	Ubuntu 22.04.2 LTS
This copy of QGIS writes debugging output.
Active Python plugins
AppendFeaturesToLayer	2.0.0
InvisibleLayersAndGroups	2.1
asistente_ladm_col	5.0.0-dev
QgisModelBaker	6.3.2.1
multilayerselect	1.5.0
valuetool	3.0.15
quick_map_services	0.19.33
LoadThemAll	3.5.0-beta-2403011
processing	2.12.99
grassprovider	2.12.99
db_manager	0.1.20
MetaSearch	0.3.6

QGIS version 3.37.0-Master QGIS code revision [066da2e1002](https://github.com/qgis/QGIS/commit/066da2e1002) Qt version 5.15.3 Python version 3.10.12 GDAL/OGR version 3.4.1 PROJ version 8.2.1 EPSG Registry database version v10.041 (2021-12-03) GEOS version 3.11.1-CAPI-1.17.1 SQLite version 3.37.2 PDAL version 2.3.0 PostgreSQL client version 14.11 (Ubuntu 14.11-0ubuntu0.22.04.1) SpatiaLite version 5.0.1 QWT version 6.1.4 QScintilla2 version 2.11.6 OS version Ubuntu 22.04.2 LTS

This copy of QGIS writes debugging output.

Active Python plugins
AppendFeaturesToLayer
2.0.0
InvisibleLayersAndGroups
2.1
multilayerselect
1.5.0
valuetool
3.0.15
quick_map_services
0.19.33
LoadThemAll
3.5.0-beta-2403011
processing
2.12.99
grassprovider
2.12.99
db_manager
0.1.20
MetaSearch
0.3.6

Supported QGIS version

• I'm running a supported QGIS version according to the roadmap.

New profile

• I tried with a new QGIS profile

Additional context

More context: #56147, #56121 and #56017