Cross-reference GDScript built-in rounding methods to ease discovery

This closes #19315.

(cherry picked from commit 20d0f5bbd714f80e22e3bd41d6506bf828c29eac)

modules/gdscript/doc_classes/@GDScript.xml

@@ -167,6 +167,7 @@
 				i = ceil(1.45)  # i is 2
 				i = ceil(1.001) # i is 2
 				[/codeblock]
+				See also [method floor], [method round], and [method stepify].
 			</description>
 		</method>
 		<method name="char">
@@ -347,6 +348,7 @@
 				# a is -3.0
 				a = floor(-2.99)
 				[/codeblock]
+				See also [method ceil], [method round], and [method stepify].
 				[b]Note:[/b] This method returns a float. If you need an integer, you can use [code]int(s)[/code] directly.
 			</description>
 		</method>
@@ -1042,6 +1044,7 @@
 				[codeblock]
 				round(2.6) # Returns 3
 				[/codeblock]
+				See also [method floor], [method ceil], and [method stepify].
 			</description>
 		</method>
 		<method name="seed">
@@ -1157,6 +1160,7 @@
 				stepify(100, 32) # Returns 96
 				stepify(3.14159, 0.01) # Returns 3.14
 				[/codeblock]
+				See also [method ceil], [method floor], and [method round].
 			</description>
 		</method>
 		<method name="str" qualifiers="vararg">