Migrate to single sln file + slnf files (#23581)

AspNetCore.sln

docs/BuildFromSource.md

eng/tools/startvs.cmd

eng/tools/tools.sln

eng/tools/tools.slnf

src/Analyzers/Analyzers.sln

src/Analyzers/Analyzers.slnf

src/Analyzers/startvs.cmd

src/Antiforgery/Antiforgery.sln

src/Antiforgery/Antiforgery.slnf

src/Antiforgery/startvs.cmd

src/Azure/Azure.sln

src/Azure/Azure.slnf

src/Azure/startvs.cmd

src/Components/Components.sln

src/Components/Components.slnf

src/Components/ComponentsNoDeps.slnf

src/Components/startvs.cmd

src/DataProtection/DataProtection.sln

src/DataProtection/DataProtection.slnf