V3: Do not encode WEBP images exceeding max dimensions

[JimBobSquarePants]

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Description

Fixes #2920

[Copilot]

Pull Request Overview

This PR introduces a new strategy to prevent encoding WEBP images whose dimensions exceed a maximum threshold. Key changes include:

• Adding a new exception throwing method in WebpThrowHelper.
• Introducing a dimension check in WebpEncoderCore to preemptively reject oversized images.
• Removing redundant dimension validation in Vp8LEncoder and modifying the JPEG encoder behavior for consistency.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/ImageSharp/Formats/Webp/WebpThrowHelper.cs	Added ThrowDimensionsTooLarge method to report oversized WEBP images.
src/ImageSharp/Formats/Webp/WebpEncoderCore.cs	Inserted a check to call the new throw helper for oversized dimensions.
src/ImageSharp/Formats/Webp/Lossless/Vp8LEncoder.cs	Removed duplicate dimension guard previously present in WriteImageSize.
src/ImageSharp/Formats/Jpeg/JpegEncoderCore.cs	Updated the dimension check condition to use '>' instead of '>=' for improved consistency.

Comments suppressed due to low confidence (1)

src/ImageSharp/Formats/Webp/Lossless/Vp8LEncoder.cs:374

• The removal of explicit dimension checks in WriteImageSize should be validated to ensure that higher-level checks reliably prevent oversized images across all code paths.

Guard.MustBeLessThan(inputImgWidth, WebpConstants.MaxDimension, nameof(inputImgWidth));