ci: use npm 7 in ci + install shx in ci

Author: aminya

script/vsts/platforms/templates/preparation.yml

@@ -30,9 +30,13 @@ steps:
       force32bit: $(IsWinX86)
     displayName: Install Node.js 12.18.3
 
-  - script: npm install --global npm@6.14.8
+  - script: npm install --global npm@7
     displayName: Update npm
 
+  # papm uses this. TODO use npx instead of directly calling shx
+  - script: npm install --global shx
+    displayName: Install shx
+
   - pwsh: |
       cd script/vsts
       npm install