Enable SiteExtensions build in VMR Pass 2

[wtgodbe]

Should cover the rest of #60146

Test build: https://dev.azure.com/dnceng/internal/_build/results?buildId=2666582&view=results

Had to do some msbuild trickery to get the build ordering correct - hooked a manual target named _VmrBuild into the SiteExtensions dependency projects, and disabled restoring w/ Nuget.Targets in pass 2 so I could hook targets before Restore

[mmitche]

If this infra was written from the ground (creating the SiteExtension package for the first time), what would we do differently?

[wtgodbe]

If this infra was written from the ground (creating the SiteExtension package for the first time), what would we do differently?

I'd consider getting rid of the meta-package (LoggingAggregate) entirely, and publishing the input x64/x86 as shipping packages instead. I believe the meta-package is just a convenience to allow devs to only have to reference one thing (CC @BrennanConroy for confirmation).

[BrennanConroy]

I assume we have both x86 and x64 in the same package because we wanted to make it easier for people using it in Azure App Service. Since you could run your site as either x86 or x64 it was nicer to have a single package with both so they didn't need to make sure they picked the right one.

[wtgodbe]

In that case maybe we'd get rid of the x64 and x86 packages (which are nonshipping) and bundle their logic into the LoggingAggregate package