do not handle thunking of intiialisation expression using "function wrapper"

[michaelficarra]

A much better way to do it is to capture the ECMAScript code itself as well as the current environment record. Save that, then it can be evaluated later. Additionally, this will clarify that constructor parameters, arguments, and new.target are all not available. Something special will have to be done regarding this for instance properties.

[jeffmo]

This is now how the proposal is specified: https://jeffmo.github.io/es-class-public-fields/#initialize-public-instance-fields