glTF importer fixes

[tarcila]

Fix glTF importer with:

• multi-UV handling
• normal scale applied AFTER decoding
• byte indices instead of just short and int indices
• strided accessors for cases where data can be interleaved
• missing-normal where normals are to be deduced from the geometry

[Copilot]

Pull request overview

This PR updates the glTF importer and shared tangent-generation utilities to better handle real-world glTF assets, including multiple UV sets, more index formats, strided/interleaved accessors, and improved tangent/normal-map handling.

Changes:

• Add support for selecting among multiple TEXCOORD_n sets when wiring textures/material samplers.
• Improve mesh attribute ingestion by using stride-aware accessor copies and supporting UNSIGNED_BYTE indices.
• Extend tangent reconstruction to support optional normal input, optional V-flip, and optional face-varying tangent outputs.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
tsd/src/tsd/io/importers/import_GLTF.cpp	Adds multi-UV wiring, strided accessor copying helpers, expanded index handling, and updated tangent reconstruction logic.
tsd/src/tsd/io/importers/detail/importer_common.hpp	Extends calcTangentsForTriangleMesh() API with defaults for texcoord Y-flip and face-varying tangents.
tsd/src/tsd/io/importers/detail/importer_common.cpp	Implements optional texcoord Y-flip and face-varying tangent output in tangent generation.

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[jeffamstutz]

LGTM, thanks!