[build] Override default yaml checkout behavior (#3157)

We're hitting a couple of git related issues on certain machines, most
commonly around submodule updating on Windows. Rather than relying on an
msbuild setup task to do this, we should override the default pipeline
source checkout behavior. We'll now fetch a clean tree and recursively
clone all relevant submodules for each build stage.

build-tools/automation/azure-pipelines.yaml

@@ -25,6 +25,10 @@ stages:
     timeoutInMinutes: 60
     cancelTimeoutInMinutes: 5
     steps:
+    - checkout: self
+      clean: true
+      submodules: recursive
+
       # Ensure the correct Mono.Cecil reference overrides are set before creating the bundle.
     - script: make prepare-props V=1 CONFIGURATION=$(XA.Build.Configuration) MSBUILD_ARGS="$(AutoProvisionArgs) $(MSBuildAbiArgs)"
       displayName: make prepare-props
@@ -76,6 +80,10 @@ stages:
     variables:
       JAVA_HOME: /Library/Java/JavaVirtualMachines/jdk1.8.0_144.jdk/Contents/Home/
     steps:
+    - checkout: self
+      clean: true
+      submodules: recursive
+
     - task: DownloadPipelineArtifact@1
       inputs:
         artifactName: $(BundleArtifactName)
@@ -142,6 +150,10 @@ stages:
     timeoutInMinutes: 360
     cancelTimeoutInMinutes: 5
     steps:
+    - checkout: self
+      clean: true
+      submodules: recursive
+
     - task: DownloadPipelineArtifact@1
       inputs:
         artifactName: $(BundleArtifactName)