Polished up full screen detection logic (Windows only)

[bsclifton]

Polished up full screen detection logic (Windows only)

• Full screen mode shows button as restore
• Clicking the restore button (when full screen) will:
  • Undo full screen
  • Restore window back to the non-maximized size

Fixes #4416

Extra notes captured (below) since this is late into 0.12.3

Auditors: @alexwykoff @bbondy

Test Plan

1. Launch Brave and make sure your window is not maximized
2. Go into full screen mode (F11)
3. Notice the caption button for maximize/restore. It should be set as restore button.
4. Hit the restore button
5. Notice status of window and caption buttons:
   • window should no longer be "full screen"
   • window should be back to original size
   • maximize button should match the status (single square for not-maximized)
6. Use maximize caption button to maximize window
7. Once maximized, hit F11 to enter full screen mode
8. Push the restore button and confirm:
   • window should no longer be "full screen"
   • window should now be smaller
   • maximize button should match the status (single square for not-maximized)

Notes about existing behavior

• You can double click any draggable area to maximize the window (executes different code than clicking the caption buttons)
• If window is full screen (via F11):
  • you can NOT drag the window (this is expected)
  • you can NOT double click a draggable are to maximize (also expected)
• Full screen and maximize status are persisted to session

[bbondy]

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