Add desktop custom window / native window controls

[webfiltered]

Modern linux / win32 window

• Adds optional (on by default) OS window code for custom window replacement on linux / win32
  • Adjusts button size to toolbar
  • Transprent background
  • Theme-reactive - colours dictated by frontend API
• Requires Add custom window / native window controls desktop#457

Window

windowStyle.mp4

// Disable via config.json
"windowStyle": "default"

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[huchenlei]

Let's split the context menu change and menu style change to 2 separate PRs.

[webfiltered]

I wanted to do that but it's a rebase nightmare somehow. The pre-commit hooks just auto-aborted the very last step of two rebases in a row... extremely frustrating. I'm disabling husky completely - should be done soon.