Add Python bindings for string literal support in AST (#13073)

Depends on #13061
Add Python bindings for string scalar support in AST
Add unit test for string comparison - column vs column, column vs literal.

Authors:
  - Karthikeyan (https://github.com/karthikeyann)
  - Vyas Ramasubramani (https://github.com/vyasr)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)
  - Ashwin Srinath (https://github.com/shwina)

URL: #13073