Nb/show notebooks as untitled (#6376)

* open notebooks as untitled files and removed the saving to home directory

* return just filename without extension since save is adding the .ipynb ext

* Changes to open bdc notebooks as untitled docs. Updated tests to align with the changes

* changes: not to show untitled file as dirty and cleaned up tests in notebookService

* changes to address untitled name conflicts with open editors.

* comment cleanup

src/sql/workbench/api/browser/mainThreadNotebookDocumentsAndEditors.ts

@@ -460,6 +460,9 @@ export class MainThreadNotebookDocumentsAndEditors extends Disposable implements
 			let untitledModel = await input.textInput.resolve();
 			await untitledModel.load();
 			input.untitledEditorModel = untitledModel;
+			if (options.initialDirtyState === false) {
+				input.untitledEditorModel.setDirty(false);
+			}
 		}
 		let editor = await this._editorService.openEditor(input, editorOptions, viewColumnToEditorGroup(this._editorGroupService, options.position));
 		if (!editor) {