"Exclude from Position Files" attribute wiped when updating from schematic

Description

The "exclude from position files" flag can currently only be set from the PCB editor, and it is always cleared (reset) when running an Update from Schematic.

While further conversation is needed on how to drive this attribute from the schematic if that workflow is preferred; at minimum it needs to be preserved when updating from schematic.

Steps to reproduce

1. Attempt to exclude a footprint from position files
2. Update board from schematic

KiCad Version

Application: KiCad PCB Editor x86_64 on x86_64

Version: (7.0.0-rc1-188-g62649b868c), release build

Libraries:
	wxWidgets 3.2.1
	FreeType 2.12.1
	HarfBuzz 5.3.1
	FontConfig 2.14.0

Platform: macOS Monterey Version 12.6 (Build 21G115), 64 bit, Little endian, wxMac

	wxWidgets: 3.2.1 (wchar_t,wx containers)
	Boost: 1.80.0
	OCC: 7.6.3
	Curl: 7.77.0
	ngspice: 38
	Compiler: Clang 13.0.0 with C++ ABI 1002

Build settings:
	KICAD_SPICE=ON