Always run the worksheet after all changes have been applied

In 23785e6, we moved worksheet.run()
from didSave to willSave since didSave is not called when the document
is not dirty, unfortunately this gives the wrong behavior when the
document _is_ dirty: it means we're going to send a run worksheet
request to the server before the server has seen all the changes to the
document, in particular with multi-line output this means that the
server will see the output with the added empty lines, which means the
line numbers in worksheet/publishOutput will be wrong. To avoid this
issue we now run the worksheet either on willSave or didSave depending
on whether the document is dirty or not.

To reproduce the issue, you can create a worksheet with:

```
val x = """

"""

"hi"
```

in it, then save the document multiple times.

Author: smarter

vscode-dotty/src/worksheet.ts

@@ -23,6 +23,13 @@ export const worksheetRunKey = "dotty.worksheet.run"
  */
 export const worksheetCancelKey = "dotty.worksheet.cancel"
 
+/**
+ * If true, the setting for running the worksheet on save is enabled.
+ */
+function runWorksheetOnSave(): boolean {
+  return vscode.workspace.getConfiguration("dotty").get("runWorksheetOnSave") as boolean
+}
+
 /**
  * A wrapper around the information that VSCode needs to display text decorations.
  *
@@ -338,11 +345,25 @@ export class WorksheetProvider implements Disposable {
       codeLensProvider,
       vscode.languages.registerCodeLensProvider(documentSelector, codeLensProvider),
       vscode.workspace.onWillSaveTextDocument(event => {
-        const runWorksheetOnSave = vscode.workspace.getConfiguration("dotty").get("runWorksheetOnSave")
-        const worksheet = this.worksheetFor(event.document)
+        const document = event.document
+        const worksheet = this.worksheetFor(document)
         if (worksheet) {
           event.waitUntil(Promise.resolve(worksheet.prepareRun()))
-          if (runWorksheetOnSave) worksheet.run()
+          // If the document is not dirty, then `onDidSaveTextDocument` will not
+          // be called so we need to run the worksheet now.
+          // On the other hand, if the document _is_ dirty, we should _not_ run
+          // the worksheet now because the server state will not be synchronized
+          // with the client state, instead we let `onDidSaveTextDocument`
+          // handle it.
+          if (runWorksheetOnSave() && !document.isDirty) {
+            worksheet.run()
+          }
+        }
+      }),
+      vscode.workspace.onDidSaveTextDocument(document => {
+        const worksheet = this.worksheetFor(document)
+        if (worksheet && runWorksheetOnSave()) {
+          worksheet.run()
         }
       }),
       vscode.workspace.onDidCloseTextDocument(document => {