create index for jsontests

Dynamically generate a file that lists all test suites in
I don't know how `async_schemas.spec.ts` worked before this.

scripts/jsontests.js

@@ -30,3 +30,9 @@ for (const suite in testSuitePaths) {
     .reduce((list, f) => list + f)
   fs.writeFileSync(`./spec/_json/${suite}.js`, `module.exports = [${code}\n]\n`)
 }
+
+const requires = Array.from(Object.keys(testSuitePaths), (s) => `require('./${s}')`)
+fs.writeFileSync(`./spec/_json/index.js`, `
+  // generated from ${__filename}
+  module.exports = [${requires.join(",\n")}]
+`)