Standardize CodeBlock component

Summary:
Code blocks are quite common in Flipper, and a bit verbose in Ant, so let's standardize!

Changelog: Standardize CodeBlock component

Reviewed By: passy

Differential Revision: D28117560

fbshipit-source-id: 5a5538a49b59ef40c814d22055fac56e7598cbbb

desktop/flipper-plugin/src/__tests__/api.node.tsx

@@ -28,6 +28,7 @@ test('Correct top level API exposed', () => {
   // Note, all `exposedAPIs` should be documented in `flipper-plugin.mdx`
   expect(exposedAPIs.sort()).toMatchInlineSnapshot(`
     Array [
+      "CodeBlock",
       "DataDescription",
       "DataFormatter",
       "DataInspector",