Link leaveCallback does not fire when links are on the edge of the terminal

[Tyriar]

See microsoft/vscode#66421

This is caused because MouseZoneManager only listened to mousemove, it should also register a listener for when the mouse leaves this._terminal.element

Code pointer:

xterm.js/src/ui/MouseZoneManager.ts

Line 99 in 2edf02e

this._terminal.element.removeEventListener('mousemove', this._mouseMoveListener);

[Tyriar]

This workaround in vscode can be removed after this is fixed microsoft/vscode#66576