Support workspace.save(URI) and workspace.saveAs(URI)

[tsmaeder]

What it does

Fixes #13352

Contributed on behalf of STMicroelectronics

How to test

The attached vsix contributes two actions "Save current editor" and "Save As current editor". They invoke "save" and "saveAs" on the currently opened editor and displays the resulting uri. Note that in contrast to VS Code, Theia does not documents as "saveable" if they are not dirty, therefore a save on a clean document will not succeed. Check that the behaviour is correct in various scenarios.

Follow-ups

Review checklist

• [x] 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

[tsmaeder]

Here's the plugin:

testsave-0.0.1.zip

And here's the source:

testsave..src.zip