osc: use custom symbols for window controls

I was recently informed that unicode has official symbols for
window controls, and I put together a change to use them, which
worked, as long as a suitable font was installed. However, it's
not that hard to get a normal system that lacks an appropriate
font, and libass wants to print warnings if the symbols aren't
in the default font, which will almost always be true.

So, I gave up and added the symbols to the custom osd font that
we already have. This ensures they are always available, and
that they are aligned consistently on all platforms.

I took the symbols from the `symbola` font, as this has a suitable
licence and the symbols look nice enough.

Symbola Licence:

    Fonts are free for any use; they may be opened, edited,
    modified, regenerated, packaged and redistributed.

Finally, as we now have access to an un-maximize symbol, I added
logic to use it when the window is maximized.

1 files changed, 20 insertions, 0 deletions

diff --git a/TOOLS/mpv-osd-symbols.sfdir/uniE113.glyph b/TOOLS/mpv-osd-symbols.sfdir/uniE113.glyph
new file mode 100644
index 0000000000..6319b8f5d9
--- /dev/null
+++ b/TOOLS/mpv-osd-symbols.sfdir/uniE113.glyph
@@ -0,0 +1,20 @@
+StartChar: uniE113
+Encoding: 57619 57619 31
+Width: 622
+VWidth: 1178
+Flags: HW
+LayerCount: 2
+Fore
+SplineSet
+768 42 m 5
+ 0 42 l 5
+ 0 746 l 5
+ 768 746 l 5
+ 768 42 l 5
+704 106 m 5
+ 704 618 l 5
+ 64 618 l 5
+ 64 106 l 5
+ 704 106 l 5
+EndSplineSet
+EndChar