* [dotnet] rename workload to Microsoft.NET.Sdk._platform_.Manifest-6.0.100
Context: https://github.com/dotnet/designs/pull/188/files#diff-8fcaa29d8e6f00b34b3cb1830d93f33e75f04424780a66a3c658c7021048e74fR125
Context: https://github.com/xamarin/xamarin-android/pull/5898
The `$(PackageId)` of our workload `.nupkg` needs to be:
Microsoft.NET.Sdk._platform_.Manifest-6.0.100
While the `$(PackageVersion)` remains the same as before.
The layout on disk will change to:
dotnet\sdk-manifests\6.0.100\Microsoft.NET.Sdk._platform_\
WorkloadManifest.json
WorkloadManifest.targets
Note that `.Manifest` and `-6.0.100` are not in the folder name on disk.
At the same time, let's also update the `version` in
`WorkloadManifest.json` so it contains the proper version for our
workload. This used to not be possible because `version` was a `long`,
but it now is a `string` where we can put our version.
* Use $(DOTNET6_VERSION_BAND)
* Pass in -p:VersionBand to 'dotnet pack'