Document support for normal and specular maps in AnimatedSprite2D

This closes #38509.

(cherry picked from commit 8d0099f5fcb5a0366d85759673674e031683e79f)

doc/classes/AnimatedSprite.xml

@@ -5,6 +5,7 @@
 	</brief_description>
 	<description>
 		Animations are created using a [SpriteFrames] resource, which can be configured in the editor via the SpriteFrames panel.
+		[b]Note:[/b] You can associate a set of normal maps by creating additional [SpriteFrames] resources with a [code]_normal[/code] suffix. For example, having 2 [SpriteFrames] resources [code]run[/code] and [code]run_normal[/code] will make it so the [code]run[/code] animation uses the normal map.
 	</description>
 	<tutorials>
 		<link title="2D Sprite animation">https://docs.godotengine.org/en/latest/tutorials/2d/2d_sprite_animation.html</link>

doc/classes/SpriteFrames.xml

@@ -5,6 +5,7 @@
 	</brief_description>
 	<description>
 		Sprite frame library for [AnimatedSprite]. Contains frames and animation data for playback.
+		[b]Note:[/b] You can associate a set of normal maps by creating additional [SpriteFrames] resources with a [code]_normal[/code] suffix. For example, having 2 [SpriteFrames] resources [code]run[/code] and [code]run_normal[/code] will make it so the [code]run[/code] animation uses the normal map.
 	</description>
 	<tutorials>
 	</tutorials>