CHANGED: Symbol chooser search now considers custom symbol fields
Visible columns can be controlled in database libraries.
In standard KiCad libraries, we show columns for all custom fields for now.
Customizable column visibility will be added in the future.
Fixes https://gitlab.com/kicad/code/kicad/-/issues/11946
Sub-libraries allow a single-level hierarchy inside a symbol library.
This is useful for database libraries and for supporting other EDA library types where a
single file can contain multiple logical groupings of symbols.
Allows placing parts from an external database that reference symbols from another loaded library.
Includes:
- nanodbc wrapper
- database schematic library plugin
- basic tests
Fixes https://gitlab.com/kicad/code/kicad/-/issues/7436
Jon Evans