Fix warnings in project.json

PR #2493 introduced the new project.json schema. The tree has 118 files
with the old schema, which added several hundred warnings.

This change can't go in until PR #2864 does - it relies on those bug
fixes.

TestAssets/TestProjects/TestLibraryWithMultipleFrameworks/project.json

@@ -1,6 +1,6 @@
 {
   "version": "1.0.0-*",
-  "compilationOptions": {
+  "buildOptions": {
     "emitEntryPoint": false
   },
   "dependencies": {},
@@ -32,4 +32,4 @@
       }
     }
   }
-}
+}