feat: enable context-isolation

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• resolves feature request: enable context-isolation #1260
• Enabled context-isolation to mitigate security issues. ¹
• And, to use ESM (electron v28), we need to enable the context-isolation (see https://github.com/electron/electron/blob/main/docs/tutorial/esm.md)
• Fixed an issue where plugins for renderer were being loaded in the preload environment. From now on, the preload scripts and renderer scripts are completely separated.

Footnotes

1. Not all security issues are resolved: ipcRenderer is still exposed to the renderer environment. ↩

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cc @th-ch @ArjixWasTaken @Su-Yong