Context isolation bypass via contextBridge 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 both `contextIsolation` and `contextBridge` are affected. This is fixed in versions 9.0.0-beta.21, 8.2.4 and 7.2.4.