Allow hooking or disabling paste events

[Eugeny]

I'm currently handling paste myself, but it seems that it's impossible to disable xterm's internal paste handlers. The attached event handlers are irremovable, and pasteHandler isn't exported.

Could you please add an option to disable default paste handlers, or an access point to override its behaviour?

[Tyriar]

Can you listen for paste using this API and handle it on your end that way?

xterm.js/typings/xterm.d.ts

Lines 473 to 482 in b5f1c33

	/**
	* Attaches a custom key event handler which is run before keys are
	* processed, giving consumers of xterm.js ultimate control as to what keys
	* should be processed by the terminal and what keys should not.
	* @param customKeyEventHandler The custom KeyboardEvent handler to attach.
	* This is a function that takes a KeyboardEvent, allowing consumers to stop
	* propogation and/or prevent the default action. The function returns
	* whether the event should be processed by xterm.js.
	*/
	attachCustomKeyEventHandler(customKeyEventHandler: (event: KeyboardEvent) => boolean): void;

This is how VS Code does it.

[Eugeny]

Haven't considered this! Would preventDefault() here prevent the browser's paste event which you're listening to for pasteHandler though?

[Tyriar]

@Eugeny I think so, in vscode I believe only "vscode keybindings" can trigger pastes and they end up firing this to do the actual paste:

https://github.com/Microsoft/vscode/blob/0d375bf5fc3b34144fde240626603c7f0b2cfc55/src/vs/workbench/parts/terminal/electron-browser/terminalInstance.ts#L631-L634

[Eugeny]

Can confirm this works.