Cache .NET SDKs and Tools

- Cache everything under '$(Agent.ToolsDirectory)/dotnet'
  directory to speed up build. Check for changes in .NET SDK Version
  variable '$(DotNetVersion)' to invalidate and rebuild the cache next build.

azure-pipelines.yml

@@ -13,18 +13,30 @@ pool:
 
 variables:
   BuildConfiguration: Release
+  BuildTools: $(Agent.ToolsDirectory)/dotnet
+  DotNetVersion: 7.0.x
 
 jobs:
 - job: BuildBits
   displayName: Build and Test solution
   timeoutInMinutes: 60
   steps:
 
+  # Cache .NET SDKs and Tools across pipeline runs
+  - task: Cache@2
+    displayName: Cache .NET SDKs
+    inputs:
+      key: 'dotnet | "$(Agent.OS)" | "$(DotNetVersion)"'
+      restoreKeys: |
+        dotnet | "$(Agent.OS)"
+        dotnet
+      path: $(BuildTools)
+
   # Install the .NET 7 SDK (Fixes dotnet/roslyn#63780)
   - task: UseDotNet@2
     displayName: Install the .NET 7 SDK
     inputs:
-      version: 7.0.x
+      version: $(DotNetVersion)
       includePreviewVersions: true
       performMultiLevelLookup: true