Fix heap-buffer-overflow in glTF decoder accessor reads

[Sebasteuo]

Add bounds validation to all glTF accessor data copy functions to prevent out-of-bounds heap reads when processing crafted .glb/.gltf files with malicious byteOffset, byteLength, or byteStride values.

The glTF decoder trusted accessor/bufferView fields from the input file without validating them against the actual buffer size. A crafted .glb file could cause memcpy to read past the end of the allocated buffer, leading to heap-buffer-overflow (confirmed via AddressSanitizer).

Affected functions:

• TinyGltfUtils::CopyDataAsFloatImpl() in tiny_gltf_utils.h
• CopyDataAsUint32() in gltf_decoder.cc
• CopyDataAs() (both specializations) in gltf_decoder.cc
• CopyDataFromBufferView() in gltf_decoder.cc

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[Sebasteuo]

@googlebot I fixed this

[Sebasteuo]

Thanks for confirming the impact and advocating for the fix to land. Quick clarification on authorship**: I am the author of PR #1165 (handle @Sebasteuo)**. The CLA is now signed, so the maintainers can proceed with review. Happy to coordinate if you have additional test cases or related findings.