* Update member-expression-to-functions
1. Babel using British spellings, so `memoise`
2. Provide a helper `AssignmentMemoiser` class, which will assign the memo'd value with the `n`th access.
* Private properties!
* Fixes
* Tests
* Update helper name
* Fix privates that reference other privates
* Don't extend a builtin
* Rebase
* Implement MemberExpressionToFunctions helper
Fixes#7733.
This will also be used to simplify the Private Fields transform, which had [almost the same code](ccd941057a/packages/babel-plugin-proposal-class-properties/src/index.js (L114-L217)) hand written.
* Cleanup
* Little more comment cleanup
* Use unary plus
This can't be redefined, unlike the `Number` identifier.
* Review comments
* Remove unused deps
