Allow external copying files into the workspace on markdown drop / paste (#182572)

Allow copying files in the workspace on markdown drop / paste

Fixes #157043

Also:

- Renames the markdown paste settings and makes them no longer experimental
- Makes the copyFiles setting no longer experimental
- Adds a `markdown.copyFiles.overwriteBehavior` which lets you control if/how existing files are overwritten

extensions/markdown-language-features/src/util/document.ts

@@ -0,0 +1,30 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as vscode from 'vscode';
+import { Schemes } from './schemes';
+import { Utils } from 'vscode-uri';
+
+export function getDocumentDir(document: vscode.TextDocument): vscode.Uri | undefined {
+	const docUri = getParentDocumentUri(document);
+	if (docUri.scheme === Schemes.untitled) {
+		return vscode.workspace.workspaceFolders?.[0]?.uri;
+	}
+	return Utils.dirname(docUri);
+}
+
+export function getParentDocumentUri(document: vscode.TextDocument): vscode.Uri {
+	if (document.uri.scheme === Schemes.notebookCell) {
+		for (const notebook of vscode.workspace.notebookDocuments) {
+			for (const cell of notebook.getCells()) {
+				if (cell.document === document) {
+					return notebook.uri;
+				}
+			}
+		}
+	}
+
+	return document.uri;
+}