#361 | adding warning messages on mutable method invocations on immutable collection

[naren2605]

fix realted to issue#361
context:
ide's like intellij show warnings on using immutable methods, incorporating warnings in our extension aswell.
created draft pr for initial review :

• logic to verify and show warnings on mutable methods invocation with test cases
  • attached intellij warnings and new change warnings in vscode extension screenshots
• other methods/collections to be added for the mutable method checks
• final content for warning messages