Add button to pop out plugins panel

The draggable plugins panel is impossible to discover for new users.
The added button pops out the plugins panel without opening it fully,
so that users can realize that the panel exists and is draggable.

vspreview/main/window.py

@@ -19,7 +19,7 @@
 
 from ..core import (
     PRELOADED_MODULES, AbstractQItem, ArInfo, CroppingInfo, DragNavigator, ExtendedWidget, Frame, GraphicsImageItem,
-    GraphicsView, HBoxLayout, MainVideoOutputGraphicsView, QAbstractYAMLObjectSingleton, StatusBar, Time, Timer,
+    GraphicsView, HBoxLayout, MainVideoOutputGraphicsView, PushButton, QAbstractYAMLObjectSingleton, StatusBar, Time, Timer,
     VBoxLayout, VideoOutput, _monkey_runpy_dicts, apply_plotting_style, dispose_environment, get_current_environment,
     make_environment
 )
@@ -192,6 +192,18 @@ def __init__(self, config_dir: SPath, no_exit: bool, reload_enabled: bool, force
 
         Plugins(self)
 
+        def pop_out_plugins():
+            left, right = self.main_split.sizes()
+            if right:
+                new_sizes = [left + right, 0]
+            else:
+                min_right = int((left + right) * 0.2)
+                new_sizes = [min(left, left + right - min_right), max(right, min_right)]
+            self.main_split.setSizes(new_sizes)
+            self.plugins.update()
+
+        self.toolbars.main.layout().addWidget(PushButton("Plugins", clicked=pop_out_plugins))
+
         self.app_settings.tab_widget.setUsesScrollButtons(False)
         self.app_settings.setMinimumWidth(
             int(len(self.toolbars) * 1.05 * self.app_settings.tab_widget.geometry().width() / 2)