Need logging to explain changes to the plugins spec

Basically people are going to complain because the output from babel after updating may be larger than before because the defaults are spec behavior.

- If they use the plugin explicitly, we can opt-into "loose" for them
- If they don't, we just need to warn that the default is "spec" or "loose", etc.

Example:
-`template-literals` - default was previously "spec" -> `'a' + b` -> `"a".concat(b)`

No file, test, or entry point is named. Start by locating the upgrade tool's handling of explicitly configured plugins and their defaults, then trace how it reports changes; done means users are warned when defaults such as "spec" or "loose" may make Babel output larger.

Written by the indexing model from the issue text.