Add licenseXml property to License and LicenseAddition

Resolves #359

Signed-off-by: Gary O'Neall <gary@sourceauditor.com>

model/ExpandedLicensing/Classes/License.md

@@ -47,3 +47,7 @@ A License represents a license text, whether listed on the SPDX License List
   - type: xsd:string
   - minCount: 0
   - maxCount: 1
+- licenseXml
+  - type: xsd:string
+  - minCount: 0
+  - maxCount: 1

model/ExpandedLicensing/Classes/LicenseAddition.md

@@ -41,3 +41,7 @@ or otherwise) which is defined by an SPDX data creator (CustomLicenseAddition).
   - type: xsd:string
   - minCount: 0
   - maxCount: 1
+- licenseXml
+  - type: xsd:string
+  - minCount: 0
+  - maxCount: 1

model/ExpandedLicensing/Properties/licenseXml.md

@@ -0,0 +1,19 @@
+SPDX-License-Identifier: Community-Spec-1.0
+
+# licenseXml
+
+## Summary
+
+Identifies all the text and metadata associated with a license in the license XML format.
+
+## Description
+
+The license XML format is defined and used by the SPDX legal team.
+See the XML fields defined at https://github.com/spdx/license-list-XML/blob/main/DOCS/xml-fields.md for a text description.
+There is also an XML schema available at https://github.com/spdx/license-list-XML/blob/main/schema/ListedLicense.xsd.
+
+## Metadata
+
+- name: standardLicenseTemplate
+- Nature: DataProperty
+- Range: xsd:string