Polish QuickInputButtonLocation (#221403)

* Fix a bug where the buttons would show up when they shouldn't by clearing them on show like the other ActionBars
* Introduce Proposed API (changed the core shape to reflect)
* Adopted in Git extension

ref https://github.com/microsoft/vscode/issues/221397

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

@@ -0,0 +1,29 @@
+/*---------------------------------------------------------------------------------------------
+ *  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/175662
+
+	export enum QuickInputButtonLocation {
+		/**
+		 * In the title bar.
+		 */
+		Title = 1,
+
+		/**
+		 * To the right of the input box.
+		 */
+		Inline = 2
+	}
+
+	export interface QuickInputButton {
+		/**
+		 * Where the button should be rendered. The default is {@link QuickInputButtonLocation.Title}.
+		 * @note This property is ignored if the button was added to a QuickPickItem.
+		 */
+		location?: QuickInputButtonLocation;
+	}
+}