SPDX enumeration value URLs could use `.` or `_` not `/` as separator

[VladimirAlexiev]

(A sub-issue of #1165)

URLs of enumeration values:

• In 2.3 used to be like this <https://spdx.org/rdf/terms/IsoAutomationLevel_conditionalAutomation>, which can be written SPARQL like spdx:IsoAutomationLevel_conditionalAutomation
• Currently they are like this <https://spdx.org/rdf/3.1/terms/Core/IsoAutomationLevel/conditionalAutomation>. Even after including per-module prefixes (eg spdx-core:) this would need to use a backslash in SPARQL: spdx_core:IsoAutomationLevel\/conditionalAutomation

Example:

• Electrical CIM enumeration values use . as separator, eg

cim:PhaseCode.N a cim:PhaseCode
cim:UnitSymbol.W a cim:UnitSymbol
eu:LimitKind.tatl a eu:LimitKind 
nc:GateLogicKind.and a nc:GateLogicKind