Documentation updates

[Logofile]

This change includes the following:

• Reverts changes made in the GitHub Actions workflow
• Adds a paragraph to the News topic about upcoming plans to announce changes to the protobuf mailing list
• Adds information to the Proto2 topic about the system checking UTF-8 validity in String fields
• Adds information to the Proto3 topic about a symbol FooEntry not being compatible with a map foo in the same scope
• Clarifies and corrects information about what is generated in Dart for enums
• Adds extensive new information to the Cross-Version Runtime Guarantee topic
• Adds information to the Version Support topic about an extension to support for Java 3.25.x
• Updates links to /programming-guides/proto2.md throughout topics
• Adds content to editions/features.md about group-like field behaviors.
• Adds content to editions/features.md about the features.(pb.cpp).string_type feature.
• Adds a new topic, reference/go/size.md
• Updates guidance on releases in support/version-support.md