Epic: Developers have access to guidance & tools that supports them in building cross-platform packages

[terrajobst]

We need to make it easier to multi-target across operating systems and architectures, which also includes better support for RID-based multi-targeting.

User Stories

• As a package author, I can use #if to perform version checks Package authors can use #if to perform version checks sdk#14540
• Completion should support preprocessor symbols Completion should support preprocessor symbols  roslyn#49694
• Package authors can multi-target between runtime identifiers (RID) User Story: Package authors can multi-target between runtime identifiers (RID) #5699
• Package authors can validate that their multi-targeted packages are well-formed User Story: Package authors can validate that their multi-targeted packages are well-formed #5700
• Package authors can validate that they didn't accidentally make an API breaking change User Story: Package authors can validate that they didn't accidentally make an API breaking change #5701
• Package authors have guidance for building multi-targeted packages User Story: Package authors have guidance for building multi-targeted packages #5702
• Package authors have guidance for building packages that deploy native code User Story: Package authors have guidance for building packages that deploy native code #5703
• As a developer, I get compile time diagnostics for unsupported APIs As a developer, I get compile time diagnostics for unsupported APIs runtime#47228
• As a package consumer, I can replace a package in my graph with a different ID and version User Story: As a package consumer, I can replace a package in my graph with a different ID and version #5864

[mairaw]

Bulk closing .NET 6 epics and user stories. If you think this issue was closed in error, please reopen the issue and update it accordingly.