This only existed as essentially a workaround for meson's behavior and
to maintain compatibility with the waf build. Since waf put everything
in a generated subdirectory, we had to put make a subdirectory called
"generated" in the source for meson so stuff could go to the right
place. Well now we don't need to do that anymore. Move the meson.build
files around so they go in the appropriate place in the subdirectory of
the source tree and change the paths of the headers accordingly. A
couple of important things to note.
1. mpv.com now gets made in build/player/mpv.com (necessary because of
a meson limitation)
2. The macos icon generation path is shortened to
TOOLS/osxbundle/icon.icns.inc.
