[vcpkg-ci-mdl-sdk] Add test port.

[jreichel-nvidia]

Add test port to prevent future regressions of mdl-sdk features, in particular for the openimageio feature, as it happened in #37489.

(I believe the unchecked items below do not really apply for new test ports.)

• 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.

[dg0yt]

Suggested change

"supports": "!x86 & !(windows & (staticcrt | arm | uwp | static)) & !(osx & arm) & !android",

Just let the test port run when mdl-sdk is supported. No need to maintain duplicate top-level restrictions.
(Restriction can be useful on a feature or dependency level, to not request unsupported dependencies.)