text: Title: Loudly deprecate variables used as embedded arguments not matching custom patterns
  Body: If you have a keyword accepting embedded arguments with a custom pattern like
  ```
  Perform ${arg:[^ ]+}
      Log To Console  ${arg}
  ```
  and use it with a variable like
  ```
  Perform ${variable}
  ```
  Robot will call the keyword regardless the variable value. This means that the keyword may be called with a value that doesn't match the explicit custom pattern. That's not great and needs to be changed.
  
  We initially planned to change this already in RF 6.0 (#4069), but it turned out that the change would cause too much backwards compatibility problems and the change was reverted. The main reason for backwards compatibility problems was that custom patterns were often used to resolve conflicts with various keyword implementations matching a keyword usage. Conflict resolution was enhanced heavily in RF 6.0 (#4454), so it is now safer to require patters to match also when using variables as embedded arguments. The change is still backwards incompatible and cannot really be done in RF 6.1, but we can now deprecate it loudly. The actual change can then be finally done in RF 7.0.