Add NavigationLink helper functions for global positions

Adds helper functions to set the links start and end position with global positions or get them as global positions.

Adds global start and end position for the navigation link to the 'link_reached' signal of NavigationAgent. That signal gets emitted when a navigation link waypoint is reached. Requires that 'owner' meta data is enabled on the NavigationAgent.

doc/classes/NavigationAgent2D.xml

@@ -171,6 +171,8 @@
 				- [code]type[/code]: Always [constant NavigationPathQueryResult2D.PATH_SEGMENT_TYPE_LINK].
 				- [code]rid[/code]: The [RID] of the link.
 				- [code]owner[/code]: The object which manages the link (usually [NavigationLink2D]).
+				- [code]link_entry_position[/code]: If [code]owner[/code] is available and the owner is a [NavigationLink2D], it will contain the global position of the link's point the agent is entering.
+				- [code]link_exit_position[/code]: If [code]owner[/code] is available and the owner is a [NavigationLink2D], it will contain the global position of the link's point which the agent is exiting.
 			</description>
 		</signal>
 		<signal name="navigation_finished">

doc/classes/NavigationAgent3D.xml

@@ -174,6 +174,8 @@
 				- [code]type[/code]: Always [constant NavigationPathQueryResult3D.PATH_SEGMENT_TYPE_LINK].
 				- [code]rid[/code]: The [RID] of the link.
 				- [code]owner[/code]: The object which manages the link (usually [NavigationLink3D]).
+				- [code]link_entry_position[/code]: If [code]owner[/code] is available and the owner is a [NavigationLink2D], it will contain the global position of the link's point the agent is entering.
+				- [code]link_exit_position[/code]: If [code]owner[/code] is available and the owner is a [NavigationLink2D], it will contain the global position of the link's point which the agent is exiting.
 			</description>
 		</signal>
 		<signal name="navigation_finished">

doc/classes/NavigationLink2D.xml

@@ -10,6 +10,18 @@
 		<link title="Using NavigationLinks">$DOCS_URL/tutorials/navigation/navigation_using_navigationlinks.html</link>
 	</tutorials>
 	<methods>
+		<method name="get_global_end_position" qualifiers="const">
+			<return type="Vector2" />
+			<description>
+				Returns the [member end_position] that is relative to the link as a global position.
+			</description>
+		</method>
+		<method name="get_global_start_position" qualifiers="const">
+			<return type="Vector2" />
+			<description>
+				Returns the [member start_position] that is relative to the link as a global position.
+			</description>
+		</method>
 		<method name="get_navigation_layer_value" qualifiers="const">
 			<return type="bool" />
 			<param index="0" name="layer_number" type="int" />
@@ -17,6 +29,20 @@
 				Returns whether or not the specified layer of the [member navigation_layers] bitmask is enabled, given a [code]layer_number[/code] between 1 and 32.
 			</description>
 		</method>
+		<method name="set_global_end_position">
+			<return type="void" />
+			<param index="0" name="position" type="Vector2" />
+			<description>
+				Sets the [member end_position] that is relative to the link from a global [param position].
+			</description>
+		</method>
+		<method name="set_global_start_position">
+			<return type="void" />
+			<param index="0" name="position" type="Vector2" />
+			<description>
+				Sets the [member start_position] that is relative to the link from a global [param position].
+			</description>
+		</method>
 		<method name="set_navigation_layer_value">
 			<return type="void" />
 			<param index="0" name="layer_number" type="int" />

doc/classes/NavigationLink3D.xml

@@ -10,6 +10,18 @@
 		<link title="Using NavigationLinks">$DOCS_URL/tutorials/navigation/navigation_using_navigationlinks.html</link>
 	</tutorials>
 	<methods>
+		<method name="get_global_end_position" qualifiers="const">
+			<return type="Vector3" />
+			<description>
+				Returns the [member end_position] that is relative to the link as a global position.
+			</description>
+		</method>
+		<method name="get_global_start_position" qualifiers="const">
+			<return type="Vector3" />
+			<description>
+				Returns the [member start_position] that is relative to the link as a global position.
+			</description>
+		</method>
 		<method name="get_navigation_layer_value" qualifiers="const">
 			<return type="bool" />
 			<param index="0" name="layer_number" type="int" />
@@ -17,6 +29,20 @@
 				Returns whether or not the specified layer of the [member navigation_layers] bitmask is enabled, given a [code]layer_number[/code] between 1 and 32.
 			</description>
 		</method>
+		<method name="set_global_end_position">
+			<return type="void" />
+			<param index="0" name="position" type="Vector3" />
+			<description>
+				Sets the [member end_position] that is relative to the link from a global [param position].
+			</description>
+		</method>
+		<method name="set_global_start_position">
+			<return type="void" />
+			<param index="0" name="position" type="Vector3" />
+			<description>
+				Sets the [member start_position] that is relative to the link from a global [param position].
+			</description>
+		</method>
 		<method name="set_navigation_layer_value">
 			<return type="void" />
 			<param index="0" name="layer_number" type="int" />