Add multiple descriptions to several classes

This pull request adds several descriptions to multiple different classes.

This improves the completeness of the documentation and enhances usability by doing so.

(cherry picked from commit 27e9df7778f9546739787caa9335636a01314877)

doc/classes/EditorPlugin.xml

@@ -409,6 +409,7 @@
 			<return type="void">
 			</return>
 			<description>
+				Minimizes the bottom panel.
 			</description>
 		</method>
 		<method name="make_bottom_panel_item_visible">
@@ -417,6 +418,7 @@
 			<argument index="0" name="item" type="Control">
 			</argument>
 			<description>
+				Makes a specific item in the bottom panel visible.
 			</description>
 		</method>
 		<method name="make_visible" qualifiers="virtual">

doc/classes/Tree.xml

@@ -205,6 +205,7 @@
 			<argument index="0" name="item" type="Object">
 			</argument>
 			<description>
+				Causes the [Tree] to jump to the specified item.
 			</description>
 		</method>
 		<method name="set_column_expand">