Support String formatting via delegate command

[CsCherrYY]

When developing the Java formatter Setting Page, a preview part is needed. However, existing format methods have the following limitation:

• Based on file. If we have a temporary file containing the preview content background, the writing or modifying on the file will trigger VS Code (maybe other clients as well) to open an editor on the temporary file. This behavior can only be avoided by calling document.save() after applying WorkspaceEdit in VS Code by now, see WorkspaceEdit without opening the file microsoft/vscode#96920. but saving the content to disk will cost more time than just keeping them in the memory.
• The current mechanism of formatting in Language Server is to monitor the modifying of the formatter profile. As a preview, the frequency of changing the settings would be frequent, which may cause saving to the local xml file many times.

Thus, I would like to offer a delegate command to support string formatting with given options.

Signed-off-by: Shi Chen chenshi@microsoft.com