Fix workbench.action.files.newUntitledFile

[msujew]

What it does

Closes #14743

The Project Manager for Java extension is using the workbench.action.files.newUntitledFile to instantly create a new untitled file and then set the language of that new file to Java (other extensions do it better btw). However, our workbench.action.files.newUntitledFile implementation used to open the quick pick instead of actually creating a new untitled file.

This change just aligns the implementation of the command to VS Code

How to test

1. Download and install the Project Manager for Java plugin
2. Open the File menu and run New File.... Select New Java File.
3. The file should open as expected and be correctly filled with some initial class construct.

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[rschnekenbu]

Looks good to me, once I understood how to use the new file > New java file menu ;) Thanks for this PR, @msujew!