Extend `EvidenceOccurrence`

[mcombuechen]

Type EvidenceOccurrence has been extended with new properties in spec 1.6.

• lineNumber
• offset
• symbol
• additionalContext

Resources:

• https://github.com/CycloneDX/specification/pull/325/files
• https://cyclonedx.org/docs/1.6/json/#components_items_evidence_occurrences

When adding these new properties to type EvidenceOccurrence, consider the conversion code for components in convert.go to achieve backwards compatibility with spec versions < v1.6.

[nscuro]

Implemented in #159