[xatlas] added new port

[Vallabh-1504]

Fixes #49976

Description:

Adds xatlas, a mesh parameterization / UV unwrapping library.
Since the upstream repository does not provide a build system, this port injects a CMakeLists.txt to build the library correctly on all platforms.

• Changes comply with the maintainer guide.
• The name of the port matches an existing name for this component on https://repology.org/ if possible, and/or is strongly associated with that component on search engines.
• Optional dependencies are resolved in exactly one way. For example, if the component is built with CMake, all find_package calls are REQUIRED, are satisfied by vcpkg.json's declared dependencies, or disabled with CMAKE_DISABLE_FIND_PACKAGE_Xxx.
• The versioning scheme in vcpkg.json matches what upstream says.
• The license declaration in vcpkg.json matches what upstream says.
• The installed as the "copyright" file matches what upstream says.
• The source code of the component installed comes from an authoritative source.
• The generated "usage text" is accurate. See adding-usage for context.
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• Only one version is in the new port's versions file.
• Only one version is added to each modified port's versions file.

[Copilot]

Pull request overview

This PR adds xatlas, a mesh parameterization/UV unwrapping library, to vcpkg. Since the upstream repository does not provide a build system, the port injects a CMakeLists.txt file to build the library correctly on all platforms.

Changes:

• Added new port for xatlas library (version 2022-07-22)
• Injected CMakeLists.txt to enable CMake build support
• Updated version database files (baseline.json and versions/x-/xatlas.json)

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
ports/xatlas/vcpkg.json	Port metadata with MIT license, homepage, and build dependencies
ports/xatlas/portfile.cmake	Build script that injects CMakeLists.txt and configures/installs the library
versions/x-/xatlas.json	Version database entry for the new port
versions/baseline.json	Baseline version entry for xatlas

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.