Adding trimTextTrailingWhitespaceCommand

[reed2ep]

#209939.
Changes include:

• Addition of "trimTextTrailingWhitespaceCommand.ts"
  This command inherits from "trimTrailingWhitespaceCommand" to provide the same behavior except in the case of
  whitespace-only lines.
• Addition of "trimTextTrailingWhitespaceCommand.test.ts"
  Since the base behavior is inherited and already tested, i elected to test just the new functionality here.
• Addition of "trimTextTrailingWhitespaceCommand to the linesOperations.ts in order for it to be added to ui.

[reed2ep]

@microsoft-github-policy-service agree

[aiday-mar]

Hi @reed2ep thank you for making this PR and apologies for the long delay. I will have a look at the PR now.

[aiday-mar]

Hi I just noticed that in the new class you added TrimTextTrailingWhitespaceCommand you added a protected method trimTrailingWhitespace. Is this method supposed to override the corresponding function in the file trimTrailingWhitespaceCommand.ts? Unfortunately the corresponding function there is not a method of the class and can not be overridden. The code in the current PR does not seem to work. I think your idea is promising but it requires more work and a refactoring of the trimTrailingWhitespaceCommand.ts file.