Add pad_image filter generating closed surfaces

[user27182]

Add new ImageDataFilter pad_image.

Partly Fully resolves #2201

Image padding will be used by #5968 to enable generating "closed" surfaces at the edges of images (otherwise regions at the edges are left open by vtkSurfaceNets).

For now the filter only implements constant padding. I'll try adding wrap and mirror but may not if those filters don't behave nicely with the current implementation. The wrap and mirror options have been added.

[user27182]

Additional info: This filter simply adds padding to the image. It can used for many applications where padding is needed.

One such use, which is a bit of a workaround in this case, is to enable generating closed surfaces as part of #5968. There, the image padding is implicit, i.e. setting image_boundaries=True will cause the input to be padded before generating the surface. It's a workaround because it's arguable this kind of functionality should be builit into the filter. See https://gitlab.kitware.com/vtk/vtk/-/issues/19170

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.97%. Comparing base (06e7a8f) to head (0458bdd).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6051      +/-   ##
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+ Coverage   96.96%   96.97%   +0.01%     
==========================================
  Files         141      141              
  Lines       24532    24624      +92     
==========================================
+ Hits        23788    23880      +92     
  Misses        744      744              

[user27182]

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[user27182]

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[tkoyama010]

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[tkoyama010]

Interesting filter. Please give me some time so I can understand the filter specs and test code.

[tkoyama010]

LGTM. Thanks!