[GStreamer] Support Dolby Vision codecs

[asurdej-comcast]

Some applications (like AppleTV+) explicitly checks MSE for DV codecs support and select proper stream based on that. Browser needs to report that Dolby vision codecs are supported.

List 'dvhe' and 'dvh1' codecs in GStreamer registry scanner but make sure they are exposed only if platform screen supports HDR.

WPEPlatform provides screen properties throuhg ScreenManager. When disabled, use fake screen properties with HDR support based on page settings.

For WPE port only.
9b6a71a

Build-Tests	Layout-Tests
✅ 🛠 wpe-246-amd64-build	✅ 🧪 wpe-246-amd64-layout
✅ 🛠 wpe-246-arm32-build	✅ 🧪 wpe-246-arm32-layout

[eocanha]

In principle, it looks good. I'll work on upstreaming it.

[eocanha]

Some updates after discussing this with @philn:

• It looks like the screenSupportsHighDynamicRange() API isn't available upstream, so this patch will be downstream-only. The ideal upstream solution would be based on the future WPE_PLATFORM API, but that's still work in project and won't be available until some WPE future release. We can do with a downstream patch by now.
• It seems that the fact of having an H.265 decoder isn't a guarantee for Dolby Vision to be supported. This means that not all the platforms should enable this Dolby Vision support. The best solution for this is to think about a Quirks related mechanism, so that we can enable the feature only for selected platforms, but being this a downstream patch, it the feature can already be controlled with the screen-supports-hdr setting. Just make sure to not ever enable it on a device whose H.265 decoder doesn't support a 10 bit colorspace profile.

[asurdej-comcast]

@eocanha Thanks for review and comments. Indeed, H265 doesn't guarantee DV support. Currently we set screen-supports-hdr setting based on the current STB and TV/HDMI capabilities. That's temporary solution before switching to WPEPlatform.
Also, we were thinking about extending boolean "screen-supports-hdr" WebKit setting with kind of enum like HDR10, DV, etc but for simplicity its left with bool as all our devices supports DV if HDR is present
Thanks