fix(@schematics/angular): add skipLibCheck to workspace tsconfig

Add skipLibCheck to speed up TypeScript analysis and prevent compilation errors caused by incompatible declaration files which were generated with older/new TS versions

Author: alan-agius4

packages/schematics/angular/workspace/files/tsconfig.json.template

@@ -8,6 +8,7 @@
     "noImplicitThis": true,
     "noFallthroughCasesInSwitch": true,
     "strictNullChecks": true,<% } %>
+    "skipLibCheck": true,
     "sourceMap": true,
     "declaration": false,
     "downlevelIteration": true,