Images: Updates the documentation with aspect-crop and decimal nuance…

[dochne]

…s for trim and draw width/height

Summary

This is documenting three changes/things that have previously not been documented correctly:

1. a new fit type named aspect-crop
2. that you can use decimals for trim
3. that you can use decimals for width/height in the context of draw

Documentation checklist

• The change adheres to the documentation style guide.

[cloudflare-docs-bot]

Review

✅ No style-guide issues found in commit 69c6c2e.

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