snap to all layers: snaps also to "footprint private" elements

Description

Not sure if this intended or not. The new feature "snap to all layers" snaps also to footprint-items which are set to "Private Layers" in the footprint definition. As these items are not shown on the pcb-editor the snapping is a little bit surprising.

OTOH this could also be seen as a feature which allows for "invisible snapping points".

Steps to reproduce

1. open attached project, open board: snap_to_all_layers.zip
2. locate R4
3. enable grid (1mm grid size), enable user.comments layer, activate top copper layer
4. activate line drawing tool, start drawing a line
5. activate new "snap all layers" mode
6. move mouse around R4, notice: the visible lines (silkscreen, fab layer, courtyard) on R4 act as snapping points (very good)
7. move mouse cursor to coordinate x/y == 10/60 or 30/60
8. observe: there are also (invisible) snapping points
9. open this footprint R4 in FP editor --> notice: there are some lines on user.comments layer, but also notice this layer is set to "footprint private"

KiCad Version

Application: KiCad PCB Editor x64 on x64

Version: 7.99.0-2304-g373fb56fb7, release build

Libraries:
	wxWidgets 3.2.2
	FreeType 2.12.1
	HarfBuzz 8.0.0
	FontConfig 2.14.2

Platform: Windows 10 (build 19045), 64-bit edition, 64 bit, Little endian, wxMSW

	wxWidgets: 3.2.2 (wchar_t,wx containers)
	Boost: 1.82.0
	OCC: 7.7.1
	Curl: 8.2.1-DEV
	ngspice: 40
	Compiler: Visual C++ 1936 without C++ ABI

Build settings: