Modify Create env API to freeze objects where applicable

[karrtikr]

• any objects are output to the consumer should have readonly properties
• such objects should be frozen as well, could use either a getter or Object.freeze

[rzhao271]

What are some verification steps for this issue?
If the issue is already covered by a TPI, feel free to label this issue as on-testplan instead.

[karthiknadig]

@rzhao271 Added author verification for this. It is not straight forward to verify this one.