Ensure we read the observable on the right input part (#291748)

Hoping to fix a layout issue reported by Harald but I don't think this is it.

src/vs/workbench/contrib/chat/browser/widget/chatWidget.ts

@@ -561,11 +561,17 @@ export class ChatWidget extends Disposable implements IChatWidget {
 		return this._attachmentCapabilities;
 	}
 
+	/**
+	 * Either the inline input (when editing) or the main input part
+	 */
 	get input(): ChatInputPart {
 		return this.viewModel?.editing && this.configurationService.getValue<string>('chat.editRequests') !== 'input' ? this.inlineInputPart : this.inputPart;
 	}
 
-	private get inputPart(): ChatInputPart {
+	/**
+	 * The main input part at the buttom of the chat widget. Use `input` to get the active input (main or inline editing part).
+	 */
+	get inputPart(): ChatInputPart {
 		return this.inputPartDisposable.value!;
 	}
 

src/vs/workbench/contrib/chat/browser/widgetHosts/viewPane/chatViewPane.ts

@@ -606,7 +606,7 @@ export class ChatViewPane extends ViewPane implements IViewWelcomeDelegate {
 
 		// When showing sessions stacked, adjust the height of the sessions list to make room for chat input
 		this._register(autorun(reader => {
-			chatWidget.input.height.read(reader);
+			chatWidget.inputPart.height.read(reader);
 			if (this.sessionsViewerVisible && this.sessionsViewerOrientation === AgentSessionsViewerOrientation.Stacked) {
 				this.relayout();
 			}