[Code] should be string interpolated to the code string

[cedvdb]

Currently using Code in an interpolated String will result in Instance of.. . In the context of macros, a more sensible option would be to override Code.toString() so string interpolatation returns a string that represents the actual code.

Use case:

Using strings is more readable than arrays in some cases. I wanted to do

RawCode.fromString('$valueReference.toIso8601String()')

but had to do:

RawCode.fromParts([valueReference, '.toIso8601String()']);

In place like here https://github.com/dart-lang/sdk/pull/57063/files#diff-e10def922b15028782e7fdcf395c5acab6f0cc2e86c1696a3e936eb775396d7aR638

[dart-github-bot]

Summary: The user wants to use a string instead of an array to represent code in the RawCode class, but the current API only accepts an array of parts. They suggest using a fromString constructor for better readability.