Bump up visibility for several helper types under JIT/Methodical (#64716)

Bump up visibility for several helper types under JIT/Methodical (#64716)

This change converts a small number of special tests to use the
[Fact] style. These tests are atypical in using various internal
types declared in their source code as fields in the test class;
bumping up test class visibility to public requires transitive
modifications to visibility of the helper types.

Thanks

Tomas