API Compat/Package Validation roadmap

[safern]

This meta issue captures the roadmap for API Compat and Package Validation.

Order of tasks is the order in which we should tackle them (they can be done simultaneously).

Sizes:
S: 1 day.
M: 2 - 3 days.
L: 1 week.
XL: 1+ weeks.

P0:

• [ApiCompat] Add assembly version check between different assets. #17365 (Size: S)
• [ApiCompatibility] Add a new rule to detect breaking changes on updating contract of abstract classes/ interfaces #17928 (Size: M)
• [API Compat] Add a rule that detects removal of abstract members #18679 (Size: S)
• [API Compat] Add rule that validates a base type or interface is not removed #18680 (Size: M) (PR [API Compat] Add rule that validates a base type or interface is not removed #18929)
• [API Compat] Add rule that prohibits sealing an inheritable type #18685 (Size: S)
• [Package Validation] Should enable API Compat strict mode when applicable #18702 (Size: S)
• [API Compat] Support suppressing an error globally for the same left and right with no target #19123 (Size: S)
• [Package Validation] Localize all the error messages and diagnostics #17366 (Size: S)
• Move PackageValidation to sdk with opt-in flag #19209 (Size: M)
• [Package Validation] Baseline package validation should run with references #18676 (Size: L)

P1:

• [API Compat] Add MSBuild task to run API Compat standalone #18677 (Needed for dotnet/runtime, wcf, etc, Size: M)
• [API Compat] Add rule to make sure nullable annotations are compatible #18681 (Size: L)
• [API Compat] Add rule to make sure virtual modifier is not removed #18682 (Size: M)
• [API Compat] Add rule to prohibit making a member virtual #18683 (Size: S)
• PackageValidation task should not filter package assets. #18165 (Size: ?)
• PackageValidation should warn if documentation files are dropped (.xml) #19614 (Size: S)

P2:

• [Package-Validation] Work required for the package validation to be on by default in sdk #18582 (Size: M)
• [Package Validation] Add support for multiple assemblies in the package. #17364 (Size: M)

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[safern]

Super seeded by: #23910