Swift: restrict field inline to only private variables

[Adarsh-NP]

This PR restricts deletion of private variables of a class but here are the regressions it will cause:

• Things inside init will not be inlined because of the new modifier node we are trying to catch.
• Why don’t we create a separate rule to clean inside init like we did for variables in function?
  • We get issues because of constructor scope collision resulting in no cleanup
• Ad-hoc variable declarations inside init will not be cleaned up.

The problem with modifiers can be solved by tweaking ts-grammar again to give the modifiers node always and then have visibility modifier as none to cover the case of declarations of just var a.

Please refer to test changes to understand more.

Land after: #613