Update libwebp to 1.6.0

[mattleibow]

Update libwebp from 1.3.2 to 1.6.0.

Changes

• Update externals/skia submodule with libwebp 1.6.0 changes
• Update cgmanifest.json version for CVE tracking

Release Notes (1.3.2 → 1.6.0)

• 1.6.0: Binary compatible. AVX2/SSE2 optimizations, WebPValidateDecoderConfig API
• 1.5.0: Binary compatible. Arm optimizations, WASM improvements, security hardening
• 1.4.0: Binary compatible. New WebPAnimEncoder chunk APIs, SharpYuv improvements

BUILD.gn Changes (in mono/skia)

• Add new libwebp_avx2 target for AVX2 lossless optimizations
• Add new palette.c source file

Local Testing

• ✅ macOS arm64 native build succeeded
• ✅ 5340 tests passed, 0 failed

Required skia PR: mono/skia#167

[github-actions]

Triage Summary

Labels will be applied to indicate the affected components, specifically the SkiaSharp backend and macOS operating system.

This issue is not a regression as it deals with updating a library and not directly related to performance or reliability of previous versions.

Additional remarks:

• The issue primarily revolves around updating the libwebp dependency related to the Skia graphics library.
• No specific label was deemed suitable for compatibility with previous versions, performance, or reliability as per the remarks.

Detailed Summary and Actions

Summary of the triage:

• The issue involves updating a dependency related to the SkiaSharp backend, specifically concerning the libwebp library.
• Successful testing on macOS arm64 indicates relevance to the macOS operating system.
• There are no concerns regarding regression, as this issue does not directly relate to compatibility, performance, or reliability.

Summary of the actions that will be performed:

Action	Item	Description
Apply Label	backend/SkiaSharp	The issue involves updating a dependency related to the Skia graphics library, primarily libwebp.
Apply Label	os/macOS	Testing indicates the issue is relevant to the macOS operating system, specifically arm64.

This entire triage process was automated by AI and mistakes may have been made. Please let us know so we can continue to improve.

[mattleibow]

/azp run

[azure-pipelines]

No pipelines are associated with this pull request.

[mattleibow]

Fixes #3464