Allow renderers capacity reevaluation

[jruesga]

This PR tries to create an implementation for #2911, by allowing the reevaluate the number of renderers allocated at mid-stream through a new RenderersFactory#reevaluateRenderers method, that allow to provide new renderers based on the information from next tracks available in the stream.
The implementation only allows to increase the number of renderers, as old renderers could potentially be in use. A new shared RenderersCoordinator class has been added to centralize the use of all renderers-related instances, so they can be growth safely mid-stream.

For example, it can be used to increment the number of metadata renderers, if a new period during mid-string contains more metadata that need to be parsed, exceeding the 2 metadata renderers provided by the default implementation. Or other use cases where dynamic allocation of renderers is required by analyzing what is in the manifest, rather than assuming a fixed number of renderers required.

override fun reevaluateRenderers(
        prevRenderers: Array<out Renderer>,
        newTrackGroups: TrackGroupArray,
        eventHandler: Handler,
        videoRendererEventListener: VideoRendererEventListener,
        audioRendererEventListener: AudioRendererEventListener,
        textRendererOutput: TextOutput,
        metadataRendererOutput: MetadataOutput
    ): Array<Renderer> {
        val renderersList = prevRenderers.toMutableList()
       
        val newMetadataRenderers = newTrackGroups.trackTypes.count { it == C.TRACK_TYPE_METADATA }
        val prevMetadataRenderers = renderersList.count { it.trackType == C.TRACK_TYPE_METADATA }
        if (newMetadataRenderers > prevMetadataRenderers) {
            for (i in prevMetadataRenderers until newMetadataRenderers) {
                renderersList.add(MetadataRenderer(metadataRendererOutput, eventHandler.looper))
            }
        }

        return renderersList.toTypedArray()
    }