Context isolation bypass via leaked cross-context objects in Electron

In Electron before versions 7.2.4, 8.2.4, and 9.0.0-beta21, there is a context isolation bypass. Code running in the main world context in the renderer can reach into the isolated Electron context and perform privileged actions. Apps using contextIsolation are affected. This is fixed in versions 9.0.0-beta.21, 8.2.4 and 7.2.4.