Enhancement: add support for bigtiff output

[chenhongtu]

Feature request

What are you trying to achieve?

I want to export tiff files larger than 4GB and need bigtiff support

When you searched for similar feature requests, what did you find that might be related?

What would you expect the API to look like?

sharp(input)
  .tiff({ bigtiff: true})
  .toFile('output_large.tif');

What alternatives have you considered?

I have considered using libvips directly to implement

Please provide sample image(s) that help explain this feature

[lovell]

This should be relatively easy, as bigtiff is an existing property of libvips' tiffsave and it should follow a similar pattern to the way miniswhite is handled. Happy to accept a PR, if you're able.

https://www.libvips.org/API/current/method.Image.tiffsave.html