JS: Add package.json files in tests relying on node_modules

We don't extract node_modules folders by default so these tests aren't
that relevant anymore, and we no longer follow node_modules resolution
rules directly.

Instead, these imports are resolved based on the monorepo support which
simply requires a package.json file to exist. There is not a good enough
reason to support node_modules directly, so we're accepting some
minor regression in these tests.

javascript/ql/test/library-tests/NPM/src/node_modules/nested/node_modules/a/package.json

@@ -0,0 +1,5 @@
+{
+    "name": "a",
+    "main": "index.js",
+    "description": "Nested version of package A"
+}

javascript/ql/test/library-tests/NPM/src/node_modules/nested/package.json

@@ -0,0 +1,3 @@
+{
+    "name": "nested"
+}