Add PasteEditProvider (#107283)

For #30066

This adds a new `documentPaste` api proposal that lets extensions hook into copy and paste.

This can be used to do things such as:

- Create link when pasting an image
- Bring along imports when copy and pasting code

src/vscode-dts/vscode.proposed.documentPaste.d.ts

@@ -0,0 +1,46 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+declare module 'vscode' {
+
+	// https://github.com/microsoft/vscode/issues/30066/
+
+	/**
+	 * Provider invoked when the user copies and pastes code.
+	 */
+	interface DocumentPasteEditProvider {
+
+		/**
+		 * Optional method invoked after the user copies text in a file.
+		 *
+		 * During {@link prepareDocumentPaste}, an extension can compute metadata that is attached to
+		 * a {@link DataTransfer} and is passed back to the provider in {@link provideDocumentPasteEdits}.
+		 *
+		 * @param document Document where the copy took place.
+		 * @param range Range being copied in the `document`.
+		 * @param dataTransfer The data transfer associated with the copy. You can store additional values on this for later use in  {@link provideDocumentPasteEdits}.
+		 * @param token A cancellation token.
+		 */
+		prepareDocumentPaste?(document: TextDocument, range: Range, dataTransfer: DataTransfer, token: CancellationToken): void | Thenable<void>;
+
+		/**
+		 * Invoked before the user pastes into a document.
+		 *
+		 * In this method, extensions can return a workspace edit that replaces the standard pasting behavior.
+		 *
+		 * @param document Document being pasted into
+		 * @param range Currently selected range in the document.
+		 * @param dataTransfer The data transfer associated with the paste.
+		 * @param token A cancellation token.
+		 *
+		 * @return Optional workspace edit that applies the paste. Return undefined to use standard pasting.
+		 */
+		provideDocumentPasteEdits(document: TextDocument, range: Range, dataTransfer: DataTransfer, token: CancellationToken): ProviderResult<WorkspaceEdit | SnippetTextEdit>;
+	}
+
+	namespace languages {
+		export function registerDocumentPasteEditProvider(selector: DocumentSelector, provider: DocumentPasteEditProvider): Disposable;
+	}
+}