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-custom.tsx

@@ -0,0 +1,17 @@
+/** @jsx jsx */
+import { createHyperscript } from 'slate-hyperscript'
+
+const jsx = createHyperscript({
+  elements: {
+    paragraph: { type: 'paragraph' },
+  },
+})
+export const input = <paragraph>word</paragraph>
+export const output = {
+  type: 'paragraph',
+  children: [
+    {
+      text: 'word',
+    },
+  ],
+}