COMP: Upgrade Windows at Azure CI from vs2017-win2016 to windows-2019

Aims to address CI errors, saying:

> ##[error]This is a scheduled windows-2016 brownout. The windows-2016 environment is deprecated and will be removed on April 1st, 2022. For more details, see actions/runner-images#5238
> ,##[error]The remote provider was unable to process the request.

Note that this means that Visual Studio 2017 is no longer tested.

Testing/CI/Azure/ci.yml

@@ -10,7 +10,7 @@ jobs:
 - job: Windows
   timeoutInMinutes: 0
   pool:
-    vmImage: 'vs2017-win2016'
+    vmImage: 'windows-2019'
   strategy:
     matrix:
       ITKv5:
@@ -27,7 +27,7 @@ jobs:
   - task: CMake@1
     displayName: 'CMake Generate ITK'
     inputs:
-      cmakeArgs: -G "Visual Studio 15 2017 Win64" -T host=x64 -DBUILD_EXAMPLES=OFF -DBUILD_TESTING=OFF -DITK_LEGACY_REMOVE=ON "$(ITK_SOURCE_DIR)"
+      cmakeArgs: -G "Visual Studio 16 2019" -T host=x64 -DBUILD_EXAMPLES=OFF -DBUILD_TESTING=OFF -DITK_LEGACY_REMOVE=ON "$(ITK_SOURCE_DIR)"
       workingDirectory: "$(ITK_BINARY_DIR)"
   - task: CMake@1
     displayName: 'CMake Build ITK'
@@ -37,7 +37,7 @@ jobs:
   - task: CMake@1
     displayName: 'CMake Generate Elastix'
     inputs:
-      cmakeArgs: -G "Visual Studio 15 2017 Win64" -T host=x64 -DITK_DIR="$(ITK_BINARY_DIR)" -DBUILD_TESTING=ON -DELASTIX_USE_GTEST=ON -DUSE_ALL_COMPONENTS=ON "$(ELASTIX_SOURCE_DIR)"
+      cmakeArgs: -G "Visual Studio 16 2019" -T host=x64 -DITK_DIR="$(ITK_BINARY_DIR)" -DBUILD_TESTING=ON -DELASTIX_USE_GTEST=ON -DUSE_ALL_COMPONENTS=ON "$(ELASTIX_SOURCE_DIR)"
       workingDirectory: "$(ELASTIX_BINARY_DIR)"
   - task: CMake@1
     displayName: 'CMake Build Elastix'
@@ -47,7 +47,7 @@ jobs:
   - task: CMake@1
     displayName: 'CMake Generate externalproject'
     inputs:
-      cmakeArgs: -G "Visual Studio 15 2017 Win64" -T host=x64 -DElastix_DIR=$(ELASTIX_BINARY_DIR) "$(ELASTIX_SOURCE_DIR)/dox/externalproject"
+      cmakeArgs: -G "Visual Studio 16 2019" -T host=x64 -DElastix_DIR=$(ELASTIX_BINARY_DIR) "$(ELASTIX_SOURCE_DIR)/dox/externalproject"
       workingDirectory: $(Agent.BuildDirectory)/externalproject-build
   - task: CMake@1
     displayName: 'CMake Build externalproject'