video: move handling of -x/-y/-xy options to VO

Now the calculations of the final display size are done after the filter
chain. This makes the difference between display aspect ratio and window
size a bit more clear, especially in the -xy case.

With an empty filter chain, the behavior of the options should be the
same, except that they don't affect vo_image and vo_lavc anymore.
options: move -geometry parsing to m_option.c

This also means the option is verified on program start, not when the VO
is created. The actual code becomes a bit more complex, because the
screen width/height is not available at program start.

The actual parsing code is still the same, with its unusual sscanf()
usage.
options: allow using % for width and height in --geometry

Now all numbers in the --geometry specification can take percentages.

Rewrite the parsing of --geometry, because adjusting the sscanf() mess
would require adding all the combinations of using and not using %. As
a side effect, using % and pixel values can be freely mixed.

Keep the aspect if only one of width or height is set. This is more
useful in general.

Note: there is one semantic change: --geometry=num used to mean setting
the window X position, but now it means setting the window width.
Apparently this was a mplayer-specific feature (not part of standard X
geometry specifications), and it doesn't look like an overly useful
feature, so we are fine with breaking it.

In general, the new parsing should still adhere to standard X geometry
specification (as used by XParseGeometry()).
video: add --autofit and --autofit-larger options

--autofit=WxH sets the window size to a maximum width and/or height,
without changing the window's aspect ratio.

--autofit-larger=WxH does the same, but only if the video size is
actually larger than the window size that would result when using
the --autofit=WxH option with the same arguments.
video: remove -x/-y/-xy options

-x/-y were rather useless and obscure. The only use I can see is
forcing a specific aspect ratio without having to calculate the aspect
ratio float value (although --aspect takes values of the form w:h).
This can be also done with --geometry and --no-keepaspect. There was
also a comment that -x/-y is useful for -vm, although I don't see how
this is useful as it still messes up aspect ratio.

-xy is mostly obsolete. It does two things: a) set the window width to
a pixel value, b) scale the window size by a factor. a) is already done
by --autofit (--autofit=num does exactly the same thing as --xy=num, if
num >= 8). b) is not all that useful, so we just drop that
functionality.
options: make --fullscreen not a global option

This was disabled in 4ea60a3 and 70c455a, when all options were still
forced file local, and resetting fullscreen was annoyingly reset when
switching to the next file. mpv keeps all options by default, so this
isn't needed anymore.
vo_vdpau: always try to native bit depth (makes 30 bit work)

Using vdpau on an X server configured to a bit depth of 30 (10 bit per
component) failed finding a visual. The cause was a hack that tried to
normalize the bit depth to 24 if it was not a known depth. It's unknown
why/if this is needed, but the following things speak against it:
- it prevented unusual bit depths like 30 bit from working
- it wasn't needed with normal bit depth like 24 bit
- it's probably copy-pasted from vo_x11 (where this code possibly makes
  sense, unlike in vo_vdpau)

Just remove this code and look for a visual with native depth.