It's hard to resize the Picture-in-Picture video window

Updates on this:

It doesn't look like setChromeMargin is what we want here. This looks like it's going to require some fiddling with the platform code to get working:

We have 2 approaches for this:

1. The first looks at having a way to set the resizable margin from the WindowUtils. To do this, we'll need to do the following:

• Expose a method on WindowUtils called setResizableMargin. SetResizableMargin takes in margin values for changing the horizontal/vertical resizer margin: aHResizerSize and aVResizerSize.

• Create an implementation for SetResizableMargin like SetChromeMargin. This function will be responsible for calling a method on nsWindow that is responsible for modifying these values mHorResizeMargin and mVertResizeMargin with aHResizerSize and aVResizerSize, respectively.

• Create a method on nsWindow called SetWindowResizerSize. As described above, it sets mHorResizeMargin and mVertResizeMargin and then calls UpdateNonClientMargins to apply other "window-y" things it needs.

• Now we need a way to prevent UpdateNonClientMargins from overwriting what we set mHorResizeMargin and mVertResizeMargin to. Right now, we should do this by storing creating another member variables on nsWindow, perhaps called mUseResizeMarginOverrides, and use this to prevent executing this code.

After all this, we should be able to do something like: pipWindow.windowUtils.setWindowResizableMargin(x, y) to increase the resizer size.

2. The second approach looks at changing what min-resize border value we use.

• Create some local variable called "minResizableBorder" whose value is initialized to kResizableBorderMinSize.
• Do a check for whether or not the window is a PiP window. I believe this is currently available by checking mAlwaysOnTop in nsWindow.
  If we're using PiP, then reassigns minResizableBorder to some other pixel value that would increase the border size significantly.
• Replace uses of kResizableBorderMinSize with minResizableBorder here: https://searchfox.org/mozilla-central/rev/26330a08b1f9d06938faa0aa5e0f8c7a58064aa2/widget/windows/nsWindow.cpp#6419-6427

I believe the first approach is what we should be exploring first due to the fact we can reuse it for other feature windows and that it seems to be using the correct variables to ensure the resizer works on different desktop resolutions, plus any other calculations nsWindow needs.