📝 Requests for Dart refactorings

[mosuem]

This is a tracker for requested refactorings in Dart. The idea is to give an overview on what is missing, suggest which refactorings might be a good first issue to tackle, and give hints on how to implement them.

For implementing an assist (i.e. a refactoring requiring no user input), refer to the tutorial or an example CL.

Good first issues for refactorings are all the analyzer-refactoring tagged issues at https://github.com/dart-lang/sdk/contribute.

cc @DanTup @dcharkes

• Make it easier to add new final fields to existing constructors #53707
• Refactoring of boolean expressions, pushing negating in #53620
• Rename(refactor) support for record's named fields #53024
• [analysis server] Refactor/quick fix to replace all usages of typedef with represented type #52846
• "Extract method" refactor should support multiple return values if records are enabled. #51990
• Refactoring operations should use var/final/const as appropriate #50018
• Extract parameter based on a value within a method #49577
• Extract widget with a child parameter #49575
• Renaming a widget should update file name when file name is same as widget #49574
• code generated local variables should be var or final based on enabled lints #49561
• extract widget refactoring should generate const constructors where appropriate #49560
• configure code generation based on enabled lints #49558
• add support for generating common functions (copyWith, to/fromMap, to/fromJson)  #48971
• Better code refactoring with regards to relative import paths #46462
• [Feature Request] New refactoring: convert positional parameters to named ones #45675
• Code Action: Generate Interface #44645
• Feature request: "Change Signature" refactoring #39842
• [feature-request] Support Extraction to superclass #36199
• [feature-request] Extract Field/Parameter #36195
• "Extract Final" / "Extract Constant" #31701
• [feature request] Extract class to a new file #30310
• Inline Method refactoring should update imports #28102
• analyzer: convert async to sync function and vice versa #23962
• Suboptimal Extract Local Variable behavior #22038
• Feature Request: Push Members Down & Safe Delete Refactor #55930
• Allow users and/or packages to create custom versions of "Wrap with ..." actions #56265