EnC: Changing the type of a locked expression should be a rude edit

[jjonescz]

• Similar to EnC: Changing the type of an expression around an active foreach statement should be a rude edit #3627

public void M()
{
    var x = new C();
    lock (x) {  }
}

When inside the lock statement body, changing from new C to new Lock or vice versa likely executes wrong unlocking code now (and probably crashes because the synthesized variables are not mapped correctly).

We should update EnC analyzer in the IDE to prohibit changes to the type of the lock expression around an active statement.

[tmat]

Fixed by #74526