Allow changing screens from non-rectangular multi-monitor setups

[vjpr]

Status

This is an incomplete draft.

Currently only implemented for up/down from a macOS primary display (my setup).

Reference

#1112

Todo

• Create a new protocol version to allow sending information about display dimensions and origins.
• Implement and test left/right.
• Implement Windows and Linux display retrieval code.
• Remove hard-coded macos-specific code from Server.cpp.
• Extract display detection code into separate functions/files.

Related Features

• Allow setting the positioning of one screen's displays relative to another screen's
  This is possible with range config setting but only for percentages at the moment.
  See links (https://symless.com/help-articles/creating-text-config-files).

Contributor Checklist:

• I have created a file in the doc/newsfragments directory IF it is a
  user-visible change (and make sure to read the README.md in that directory)