windowWillResize_toSize -> windowDidResize

[foxnne]

This PR is necessary for hexops/mach#1317 and needs to be merged first so that the build.zig.zon can be updated.

After more research, I found that windowDidResize is the better way to get the window size change, as we need to get the frame and use ContentRectForFrameRect to make sure we are getting the correct window size with respect to the titlebar. This fixes an issue where resizing the window with the mouse, and then programmatically setting the window size would yield an incorrect window size.

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