Try caching npm (#8436)

* Attempt to cache node_modules

* Change npm ci to install so we can actually cache

* Follow directions on devops docs

* Move variable and fix spacing

* Use restore cache

* Put back dependencies

Author: rchiodo

build/ci/templates/globals.yml

@@ -7,3 +7,5 @@ variables:
   VSC_PYTHON_FORCE_LOGGING: true # Enable this to turn on console output for the logger
   VSC_PYTHON_LOG_FILE: '$(Build.ArtifactStagingDirectory)/pvsc.log'
   CI_BRANCH_NAME: ${Build.SourceBranchName}
+  npm_config_cache: $(Pipeline.Workspace)/.npm
+

build/ci/templates/steps/initialization.yml

@@ -73,6 +73,16 @@ steps:
     #   displayName: 'Uninstall canvas and install build from source (only for Linux)'
     #   condition: and(succeeded(), eq(variables['Agent.Os'], 'Linux'))
 
+    # See the help here on how to cache npm
+    # https://docs.microsoft.com/en-us/azure/devops/pipelines/caching/?view=azure-devops#nodejsnpm
+    - task: CacheBeta@0
+      inputs:
+          key: npm | $(Agent.OS) | package-lock.json
+          path: $(npm_config_cache)
+          restoreKeys: |
+            npm | $(Agent.OS)
+          displayName: Cache npm
+
     - task: Npm@1
       displayName: "npm ci"
       inputs: