Merge pull request #7102 from jtattermusch/coreclr_update

src/csharp/Grpc.Auth/project.json

src/csharp/Grpc.Core.Tests/project.json

src/csharp/Grpc.Core/project.json

src/csharp/Grpc.Examples.MathClient/project.json

src/csharp/Grpc.Examples.MathServer/project.json

src/csharp/Grpc.Examples.Tests/project.json

src/csharp/Grpc.HealthCheck.Tests/project.json

src/csharp/Grpc.HealthCheck/project.json

src/csharp/Grpc.IntegrationTesting.Client/project.json

src/csharp/Grpc.IntegrationTesting.QpsWorker/project.json

src/csharp/Grpc.IntegrationTesting.Server/project.json

src/csharp/Grpc.IntegrationTesting.StressClient/project.json

src/csharp/Grpc.IntegrationTesting/project.json

templates/src/csharp/Grpc.Auth/project.json.template

templates/src/csharp/Grpc.Core/project.json.template

templates/src/csharp/Grpc.HealthCheck/project.json.template

templates/src/csharp/build_options.include

...ls/dockerfile/test/csharp_coreclr_x64/Dockerfile.template

tools/dockerfile/test/csharp_coreclr_x64/Dockerfile

tools/run_tests/build_csharp_coreclr.sh