Add strict null checks scripts to precommit and to tfs builds

build/tfs/linux/continuous-build-linux.yml

@@ -27,6 +27,9 @@ steps:
 - script: |
     yarn monaco-compile-check
   displayName: Run Monaco Editor Checks
+- script: |
+    yarn strict-null-check
+  displayName: Run Strict Null Checks
 - script: |
     yarn compile
   displayName: Compile Sources