using js-to-ts converter on JSX. (#3906)

Added 'include' parameter to tsconfig to tell the compiler to only look inside the src directory

packages/slate-hyperscript/test/fixtures/element-nested-string.tsx

@@ -0,0 +1,19 @@
+/** @jsx jsx */
+import { jsx } from 'slate-hyperscript'
+
+export const input = (
+  <element>
+    <element>word</element>
+  </element>
+)
+export const output = {
+  children: [
+    {
+      children: [
+        {
+          text: 'word',
+        },
+      ],
+    },
+  ],
+}