Add Annotations support to fmiReferences and related elements

[Copilot]

FMI and SSP both support vendor annotations on elements; FMI-LS-REF had no equivalent, creating a blocker when tool-specific metadata needed to be attached.

Imports fmi3Annotation.xsd from the FMI standard and adds the optional <Annotations> child element to all major elements in both schemas, plus documentation updates.

Schema: fmi3LayeredStandardReferenceManifest.xsd

• Import fmi3Annotation.xsd
• <fmiReferences> and <Related> now accept an optional <Annotations> child

Schema: fmi3LayeredStandardReferenceExperiments.xsd

• Import fmi3Annotation.xsd
• <Experiments>, <Experiment>, <Parameters>, <Stimuli>, and <References> now accept an optional <Annotations> child

Docs

• Updated element detail tables in docs/index.adoc for all affected elements

Example usage:

<Related type="text/modelica" source="model.mo" role="model" description="Modelica source">
  <Annotations>
    <Annotation type="com.example.tool">
      <tool:metadata xmlns:tool="com.example.tool" reviewedBy="alice"/>
    </Annotation>
  </Annotations>
</Related>

[pmai]

Add the usage example to the fmi_ls_ref_manifest_example.xml example

[Copilot]

Add the usage example to the fmi_ls_ref_manifest_example.xml example

Done in commit 3fe24b9. The first <Related> entry in the example now demonstrates an <Annotations> child with a vendor-specific <Annotation type="com.example.tool"> element.