This commit adjusts the window layer to have it try to load EGL
implementations on macOS. This is important as the system
provided OpenGL implementation is deprecated and I wanted to
have a path forward for when it is finally removed.
If EGL fails to initialize, we fall back to the CGL/OpenGL
implementation that we used previously.
I've included binaries built for 64-bit intel from the MetalANGLE
project; here's how I built them:
```
git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git --depth 1
git clone https://github.com/kakashidinho/metalangle --depth 1
cd metalangle
PATH=$PWD/../depot_tools:$PATH python scripts/bootstrap.py
PATH=$PWD/../depot_tools:$PATH gclient sync
PATH=$PWD/../depot_tools:$PATH gn --args="is_debug=false angle_enable_metal=true angle_enable_vulkan=false angle_enable_gl=false angle_build_all=false" gen out/Release
PATH=$PWD/../depot_tools:$PATH autoninja -C out/Release
```
Those steps are a little too long to want to put them directly
into the wezterm CI.
It is important for metalangle to be >= 8230df39a5
in order for scaling to be handled correctly when dragging windows
between monitors.
refs: https://github.com/kakashidinho/metalangle/issues/34
