This PR includes several small changes to global-api.md in the migration guide, including:

• Remove the Vue. prefix in examples that don't really need it. The difference between the ESM and CDN builds is covered near the top so there's no need to include that prefix in the examples that follow.
• Adjust the indentation (lines 31-42) so the example is indented to match the list.
• Change the word current to Vue 2. I assume the wording was copied from the RFC.

I think the other tweaks are probably self-explanatory but let me know if anything isn't clear.

I did want to change the Foo and Bar to more meaningful names but I don't understand that example well enough to come up with something suitable.