src/vs/workbench/api/common/extHostComments.ts/ExtHostCommentThread/collapsibleState
class ExtHostCommentThread:		set collapsibleState(newState: vscode.CommentThreadCollapsibleState) {
			this._collapseState = newState;
			this.modifications.collapsibleState = newState;
			this._onDidUpdateCommentThread.fire();
		}