fix(demo): allow switch between UITextDisplayer and SimpleTextDisplayer

[avelad]

Closes #4209

[theodab]

shaka-player/demo/main.js

Lines 1163 to 1173 in 8719bdc

	const assetConfig = asset.getConfiguration();
	if (storage) {
	storage.configure(assetConfig);
	} else {
	// Remove all not-player-applied configurations, by resetting the
	// configuration then re-applying the desired configuration.
	this.player_.resetConfiguration();
	this.player_.configure(this.desiredConfig_);
	this.player_.configure(assetConfig);
	// This uses Player.configure so as to not change |this.desiredConfig_|.
	}

Yeah, it looks like the demo config values are applied to the player inside shakaDemo.Main.drmConfiguration_, so it makes sense that this would be the correct fix.
Annoying. It's not obvious at all that that is part of that function. I should have made that a separate function, for clarity. Ah well.