move _toolbar_2 from webagg_core to webagg

Co-Authored-By: Antony Lee <1322974+anntzer@users.noreply.github.com>

Author: ianhi

lib/matplotlib/backends/backend_webagg.py

@@ -51,6 +51,10 @@ class FigureCanvasWebAgg(core.FigureCanvasWebAggCore):
     pass
 
 
+class FigureManagerWebAgg(core.FigureManagerWebAgg):
+    _toolbar2_class = core.NavigationToolbar2WebAgg
+
+
 class WebAggApplication(tornado.web.Application):
     initialized = False
     started = False
@@ -299,7 +303,7 @@ def ipython_inline_display(figure):
 @_Backend.export
 class _BackendWebAgg(_Backend):
     FigureCanvas = FigureCanvasWebAgg
-    FigureManager = core.FigureManagerWebAgg
+    FigureManager = FigureManagerWebAgg
 
     @staticmethod
     def show():

lib/matplotlib/backends/backend_webagg_core.py

@@ -453,7 +453,7 @@ def set_history_buttons(self):
 
 
 class FigureManagerWebAgg(backend_bases.FigureManagerBase):
-    _toolbar2_class = ToolbarCls = NavigationToolbar2WebAgg
+    ToolbarCls = NavigationToolbar2WebAgg
 
     def __init__(self, canvas, num):
         self.web_sockets = set()