[2.38][GST] Ensure GST initialized before playing with GST Quirks

[asurdej-comcast]

GStreamerQuirksManager verifies each quirk with isPlatformSupported() that usually relies on gst elements presense in the registry. Calling this without gst_init called fails for every gst element and rejects all quirks.

The problem exists for apps that don't use any of canPlayType() or isTypeSupported() that handle gst_init

In the case I was analyzing, with audio only live stream playback, the gst_init was called in MediaPlayerPrivateGStreamer constructor, just after isHolePunchRenderingEnabled() that initialized gst quirks singleton:

#if USE(TEXTURE_MAPPER_GL) && USE(NICOSIA)
    m_nicosiaLayer = Nicosia::ContentLayer::create(Nicosia::ContentLayerTextureMapperImpl::createFactory(*this,
        [&]() -> Ref<TextureMapperPlatformLayerProxy> {
            if (isHolePunchRenderingEnabled())
                return adoptRef(*new TextureMapperPlatformLayerProxyGL);

#if USE(TEXTURE_MAPPER_DMABUF)
            if (webKitDMABufVideoSinkIsEnabled() && webKitDMABufVideoSinkProbePlatform())
                return adoptRef(*new TextureMapperPlatformLayerProxyDMABuf);
#endif
            return adoptRef(*new TextureMapperPlatformLayerProxyGL);
        }()));
#endif

    ensureGStreamerInitialized();
    m_audioSink = createAudioSink();

internally
60d9e16

Build-Tests	Layout-Tests
✅ 🛠 wpe-238-amd64-build	✅ 🧪 wpe-238-amd64-layout
✅ 🛠 wpe-238-arm32-build	✅ 🧪 wpe-238-arm32-layout

[asurdej-comcast]

It is related to #1488