Easier opt-in for react-intl without parser

[testower]

Reference: https://formatjs.io/docs/guides/advanced-usage#react-intl-without-parser-40-smaller

Currently, it's not possible to use react-intl without parser together with unejected Create React App. There's a note in the documentation that "In the future, we'll gear towards making this the default behavior."

This seems like a sensible direction, but in the meantime, would it be possible to allow for an opt-in that doesn't require a webpack alias?

Some ideas:

• Environment variable
• Configuration option in a file or in a package.json section
• IntlProvider prop