This commit removes a large amount of code partially duplicated
between the text and the graphics windows, and opens the path to
having more than one model window on screen at any given time,
as well as simplifies platform work.
This commit also adds complete support for High-DPI device pixel
ratio. It adds support for font scale factor (a fractional factor
on top of integral device pixel ratio) on the platform side, but not
on the application side.
This commit also adds error checking to all Windows API calls
(within the abstracted code) and fixes a significant number of
misuses and non-future-proof uses of Windows API.
This commit also makes uses of Windows API idiomatic, e.g. using
the built-in vertical scroll bar, native tooltips, control
subclassing instead of hooks in the global dispatch loop, and so on.
It reinstates tooltip support and removes menu-related hacks.
This commit alters the build system substantially; it adds another
platform, `headless`, that provides stubs in place of all GUI
functions, and provides a library `solvespace_headless` alongside
the main executable. To cut down build times, only the few files
that have #if defined(HEADLESS) are built twice for the executable
and the library; the rest is grouped into a new `solvespace_cad`
library. It is not usable on its own and just serves for grouping.
This commit also gates the tests behind a -DENABLE_TESTS=ON CMake
option, ON by default (but suggested as OFF in the README so that
people don't ever have to install cairo to build the executable.)
The tests introduced in this commit are (so far) rudimentary,
although functional, and they serve as a stepping point towards
introducing coverage analysis.
