Add equivalent of wagtailimages_tags.image's "preserve-svg" argument

[jams2]

When using Wagtail's image template tag, developers can provide a preserve-svg argument (docs). When supplied, this argument will cause Wagtail to limit the filters applied to SVGs to only those that would not require rasterisation - i.e. resize and crop operations. If not supplied, attempting to apply a rasterisation-requiring operation to an SVG will result in an error being raised, as Willow cannot perform the operation.

There is no equivalent to this in grapple. If acceptable, I would like to add this functionality. It looks like it would be sufficient to add a new argument to the rendition field (here), and update the resolve_rendition method with extra conditional logic (here).

[zerolab]

Go for it @jams2

[zerolab]

[!note] Work in progress notes to self

• needs a dummy wrapper for to_svg_safe_spec() for Wagtail < 5.
  • https://github.com/wagtail/wagtail/commit/9e914dbe877a85559d49c40f16cd9a2460c22acc breaks mutations using snippets. solution inline the import in the hook registration