Properly track where a build flag is declared

This allows us to generate an error when it is then set in an earlier
location in the list.

Bug: 346883187
Test: manual
Change-Id: I1c8389ff0d5a16c080008967ab5e0b9b93101301

cmd/release_config/release_config_lib/flag_artifact.go

@@ -138,6 +138,8 @@ func (src *FlagArtifact) Clone() *FlagArtifact {
 		FlagDeclaration:  src.FlagDeclaration,
 		Traces:           src.Traces,
 		Value:            value,
+		DeclarationIndex: src.DeclarationIndex,
+		Redacted:         src.Redacted,
 	}
 }