Stable branch live runner changes

This pull request includes changes to the StableBranch for:
1. LiveRunner delta AST and string input API implementation
2. Changes to Codegen and VM to support delta AST execution
3. Merge with Jun's fixes in StableBranch
4. Inspection API in LiveRunner as an alternative to QueryNodeValue\
5. Some test cases in ProtoTest/LiveRunnerTests/MicrofeatureTests.cs (in progress)