refactor: getPluginInstance allow match by type secondary

[Aarebecca]

In a generic situation, it should pass a exact key to getPluginInstance, but sometimes it may be a little bit verbose when setting the plugin in options. Now getPluginInstance will try to find the instance after finding by the key.

Graph options:

plugins: ['fullscreen']

Get instance:

graph.getPluginInstance('fullscreen');

⚠️ Note: this is just a fallback plan, and if a plugin is configured multiple times, it only returns the first instance.