Make PersistedAssemblyBuilder public and update all references

[buyaa-n]

• Make Persisted AssemblyBuilder implementation public
• Move all related new APIs from AssemblyBuilder to into PersistedAssemblyBuilder
• Add public MetadataBuilder GenerateMetadata(out BlobBuilder ilStream, out BlobBuilder mappedFieldData); method
• Add corresponding tests
• Update references in runtime accordingly

Related to #92975
Fixes #97015

[dotnet-issue-labeler]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.