Pcb print: allow to use bounding box of selected layers

[John Beard]

1) Have a PCB with two layers: normal features on F.Cu and some text off to one side on (say) Cmts.User (eg attached PCB)
2) Print the PCB at a higher scale (say 5), selecting only F.Cu in the print dialog
3) The output will have the bounding box of the whole PCB, including the comment layer (which isn't shown)
4) This means it is difficult to print just the bit you wanted at a higher scale centred in a page.

I suggest there should be an option to use the bounding box of only the layers selected in the print dialog (rather than the current behaviour of using the bounds of ALL layers, printed or not).

This must be an option, as it's still useful to be able to print different layer stackups with identical alignments.

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Application: pcbnew
Version: (5.1.0-rc1-29-gbed066771-dirty), debug build
Libraries:
    wxWidgets 3.0.4
    libcurl/7.63.0 OpenSSL/1.1.1a zlib/1.2.11 libidn2/2.1.0 libpsl/0.20.2 (+libidn2/2.1.0) libssh2/1.8.0 nghttp2/1.36.0
Platform: Linux 4.20.6-arch1-1-ARCH x86_64, 64 bit, Little endian, wxGTK
Build Info:
    wxWidgets: 3.0.4 (wchar_t,wx containers,compatible with 2.8) GTK+ 3.24
    Boost: 1.69.0
    OpenCASCADE Community Edition: 6.9.1
    Curl: 7.63.0
    Compiler: GCC 8.2.1 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=ON
    KICAD_SCRIPTING_WXPYTHON=ON
    KICAD_SCRIPTING_WXPYTHON_PHOENIX=ON
    KICAD_SCRIPTING_ACTION_MENU=ON
    BUILD_GITHUB_PLUGIN=ON
    KICAD_USE_OCE=ON
    KICAD_USE_OCC=OFF
    KICAD_SPICE=ON

[KiCad Janitor (kicad-janitor)]

KiCad bug tracker has moved to Gitlab. This report is now available here: https://gitlab.com/kicad/code/kicad/-/issues/2338