[Bug] Async onPaste handlers not recognized

[polyrainbow]

When using an async function as an onPaste handler in a tool, the tool's pasteConfig is not recognized by editor.js. The problem is this check here. The function isFunction returns false for async functions. And this is because the function typeof returns the string asyncfunction instead of function. In my opinion, the implementation of isFunction is wrong. It should return true for async functions, because async functions are functions, too.

Steps to reproduce:

1. Import a tool whose onPaste handler is an async function
2. Paste something that matches the tool's pasteConfig

Behavior: The pasted content is pasted inside a new default block.

Expected behavior: The pasted content should be pasted inside a new block of the imported tool.