snap to object feature now only works for things on the same layer (lp:#1830164)

Original report created by Rene Poeschl (poeschlr)

I seem to remember that the snap to objects feature worked with respect to
any layer no mater which layer the snap target is on. Right now this seems
no longer to be the case.

To test this draw some lines on the edge cuts layer.

And then try to snap to that while drawing on the silk layer.

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This is also the case with the move command when the group one moves
contains things from multiple layers. Lets draw some lines on edgecuts and
one on silk as the moved objects plus a reference line on the edgecuts
layer. As long as one does not include the line on silk in the moved group
it is possible to snap to the edge cuts line. This stops working as soon as
the silk line is included.

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Application: kicad
Version: (5.1.2)-1, release build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.61.1 OpenSSL/1.1.1 (WinSSL) zlib/1.2.11 brotli/1.0.6
libidn2/2.0.5 libpsl/0.20.2 (+libidn2/2.0.5) nghttp2/1.34.0
Platform: Windows 8 (build 9200), 64-bit edition, 64 bit, Little endian,
wxMSW
Build Info:
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8)
    Boost: 1.68.0
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.61.1
    Compiler: GCC 8.2.0 with C++ ABI 1013

Build settings:
    USE_WX_GRAPHICS_CONTEXT=OFF
    USE_WX_OVERLAY=OFF
    KICAD_SCRIPTING=ON
    KICAD_SCRIPTING_MODULES=ON
    KICAD_SCRIPTING_PYTHON3=OFF
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=OFF
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON

Original tags: pcbnew