The idea is pretty simple: When `MemberImportVisibility` is enabled, we know that imports can only affect the current source file. So, we can just try and remove every single `import` declaration in the file, check if a new error occurred and if not, we can safely remove it.
Previously package manifest refactoring actions conformed to a custom
refactoring provider and produced a `PackageEdit` that, in addition to
manifest file changes, included a list of auxiliary files. This is no
longer the case and all package manifest refactoring actions are now
responsible only for manifest file transformations, the rest is handled
separately.
