Convert ProjectTemplates to build using ProjectReferences (#6935)

.gitignore

Directory.Build.props

build/buildorder.props

build/repo.props

build/repo.targets

build/submodules.props

eng/Dependencies.props

eng/targets/Packaging.targets

...ns/src/Microsoft.AspNetCore.SpaServices.Extensions.csproj

src/ProjectTemplates/Directory.Build.props

src/ProjectTemplates/Directory.Build.targets

src/ProjectTemplates/GenerateContent.targets

src/ProjectTemplates/SetPackageProperties.targets

src/ProjectTemplates/THIRD-PARTY-NOTICES

src/ProjectTemplates/TemplateProjects.props

...emplates/Microsoft.DotNet.Web.Client.ItemTemplates.csproj

...mplates/content/Less/.template.config/dotnetcli.host.json

...ItemTemplates/content/Less/.template.config/template.json

...es/Web.Client.ItemTemplates/content/Less/styleSheet1.less

...mplates/content/Scss/.template.config/dotnetcli.host.json