Tooltip: Follow the standard appendTo logic

Even though there's no reason to ever configure the parent element via an
`appendTo` option, following the standard logic is useful for scrollable
elements and native dialogs.

Fixes #10739
Closes gh-1517

ui/tooltip.js

@@ -428,7 +428,7 @@ $.widget( "ui.tooltip", {
 		this._addClass( content, "ui-tooltip-content" );
 		this._addClass( tooltip, "ui-tooltip", "ui-widget ui-widget-content" );
 
-		tooltip.appendTo( this.document[ 0 ].body );
+		tooltip.appendTo( this._appendTo( element ) );
 
 		return this.tooltips[ id ] = {
 			element: element,
@@ -446,6 +446,16 @@ $.widget( "ui.tooltip", {
 		delete this.tooltips[ tooltip.attr( "id" ) ];
 	},
 
+	_appendTo: function( target ) {
+		var element = target.closest( ".ui-front, dialog" );
+
+		if ( !element.length ) {
+			element = this.document[ 0 ].body;
+		}
+
+		return element;
+	},
+
 	_destroy: function() {
 		var that = this;