Extend tsserver interface to allow refactoring failure reporting

<!-- 🚨 STOP 🚨 𝗦𝗧𝗢𝗣 🚨 𝑺𝑻𝑶𝑷 🚨 Half of all issues filed here are duplicates, answered in the FAQ, or not appropriate for the bug tracker. Please read the FAQ first, especially the "Common Feature Requests" section. --> ## Search Terms refactoring report failure fail <!-- List of keywords you searched for before creating this issue. Write them down here so that others can find this suggestion more easily --> ## Suggestion I would like a way to report refactoring failures similar to rename fail report ("You cannot rename this element"). This change improves transparency. Edit: This might imply changes in VS Code language server extension as well. I'm not familiar with it though. <!-- A summary of what you'd like to see added or changed --> ## Use Cases This would be useful to allow refactorings to initially show the refactoring, but when invoking it, an error message should be shown, instead of just not showing the refactoring. This would be confusing to the user. <!-- What do you want to use this for? What shortcomings exist with current approaches? --> ## Examples Let's say we want to inline a variable, that is not initialized. This should not be possible. But it is still useful to show the refactoring initially, since the user may be confused why the option doesn't show up. Then, if the user wants to invoke the refactoring, they get the error message "Cannot inline uninitialized variable." ``` let notInitialized; // should not allow inlining, but tell user why foo(notInitialized); ``` <!-- Show how this would be used and what the behavior would be --> ## Checklist My suggestion meets these guidelines: * [*] This wouldn't be a breaking change in existing TypeScript / JavaScript code * [*] This wouldn't change the runtime behavior of existing JavaScript code * [*] This could be implemented without emitting different JS based on the types of the expressions * [*] This isn't a runtime feature (e.g. new expression-level syntax)