[WiX 5] Workloads

[joeloff]

.NET optional workload tasks in Arcade currently use WiX v3. As we're migrating .NET 10 to WiX v5, we should support building workloads using v5.

• Generated source templates should be updated to the new v5 schema
• Generated .wixproj files should be migrated to the new SDK style projects
• Standalone tools like candle, light, and heat no longer exist in v5. The build tasks should either invoke the wix tool directly or execute msbuild on the new projects for each workload installer.