Rect2: Clarify docs for `has_point` excluding bottom and right borders

Improve tests, as well as documentation for `expand`.

(cherry picked from commit 36c4451a7b)

doc/classes/AABB.xml

@@ -39,7 +39,14 @@
 			<return type="AABB" />
 			<argument index="0" name="to_point" type="Vector3" />
 			<description>
-				Returns this [AABB] expanded to include a given point.
+				Returns a copy of this [AABB] expanded to include a given point.
+				[b]Example:[/b]
+				[codeblock]
+				# position (-3, 2, 0), size (1, 1, 1)
+				var box = AABB(Vector3(-3, 2, 0), Vector3(1, 1, 1))
+				# position (-3, -1, 0), size (3, 4, 2), so we fit both the original AABB and Vector3(0, -1, 2)
+				var box2 = box.expand(Vector3(0, -1, 2))
+				[/codeblock]
 			</description>
 		</method>
 		<method name="get_area">

doc/classes/Rect2.xml

@@ -56,7 +56,14 @@
 			<return type="Rect2" />
 			<argument index="0" name="to" type="Vector2" />
 			<description>
-				Returns this [Rect2] expanded to include a given point.
+				Returns a copy of this [Rect2] expanded to include a given point.
+				[b]Example:[/b]
+				[codeblock]
+				# position (-3, 2), size (1, 1)
+				var rect = Rect2(Vector2(-3, 2), Vector2(1, 1))
+				# position (-3, -1), size (3, 4), so we fit both rect and Vector2(0, -1)
+				var rect2 = rect.expand(Vector2(0, -1))
+				[/codeblock]
 			</description>
 		</method>
 		<method name="get_area">
@@ -100,7 +107,8 @@
 			<return type="bool" />
 			<argument index="0" name="point" type="Vector2" />
 			<description>
-				Returns [code]true[/code] if the [Rect2] contains a point.
+				Returns [code]true[/code] if the [Rect2] contains a point. By convention, the right and bottom edges of the [Rect2] are considered exclusive, so points on these edges are [b]not[/b] included.
+				[b]Note:[/b] This method is not reliable for [Rect2] with a [i]negative size[/i]. Use [method abs] to get a positive sized equivalent rectangle to check for contained points.
 			</description>
 		</method>
 		<method name="intersects">