bootloader: Refactor console functions into the VFS ConsoleNode class.

This way it becomes much easier to write multiple console implementations
in one bootloader.

Tested for bios_ia32 and efi.

Change-Id: I67134f5c3de109b15d46898864ba7f51c6592afc
Reviewed-on: https://review.haiku-os.org/c/haiku/+/4642
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>