Use legacy image implementation when not using 9-slice image

[x2048]

Fixes #12581

To do

This PR is Ready for Review.

How to test

1. Set gui_scaling_filter = true
2. Start Repixture game
3. Open inventory
4. Notice that inventory slots do not have dark border (see Inventory slots in Repixture look different in 5.6.0-dev (with gui_scaling_filter = true) #12581).

[SmallJoker]

This could also be fixed the other way around: by specifying whether or not to scale&filter GUIAnimatedImage:

diff --git a/src/gui/guiAnimatedImage.cpp b/src/gui/guiAnimatedImage.cpp
index 890763e71..d68009085 100644
--- a/src/gui/guiAnimatedImage.cpp
+++ b/src/gui/guiAnimatedImage.cpp
@@ -36,8 +36,12 @@ void GUIAnimatedImage::draw()
 	if (m_middle.getArea() == 0) {
 		const video::SColor color(255, 255, 255, 255);
 		const video::SColor colors[] = {color, color, color, color};
-		draw2DImageFilterScaled(driver, m_texture, AbsoluteRect, rect, cliprect,
-			colors, true);
+		if (m_scale_image) {
+			driver->draw2DImage(m_texture, AbsoluteRect, rect, cliprect, colors, true);
+		} else {
+			draw2DImageFilterScaled(driver, m_texture, AbsoluteRect, rect, cliprect,
+				colors, true);
+		}
 	} else {
 		draw2DImage9Slice(driver, m_texture, AbsoluteRect, rect, m_middle, cliprect);
 	}
diff --git a/src/gui/guiAnimatedImage.h b/src/gui/guiAnimatedImage.h
index 885aedece..d66a4cca1 100644
--- a/src/gui/guiAnimatedImage.h
+++ b/src/gui/guiAnimatedImage.h
@@ -16,6 +16,8 @@ class GUIAnimatedImage : public gui::IGUIElement {
 	void setTexture(video::ITexture *texture) { m_texture = texture; };
 	video::ITexture *getTexture() const { return m_texture; };
 
+	void setScaleImage(bool do_scale) { m_scale_image = do_scale; }
+
 	void setMiddleRect(const core::rect<s32> &middle) { m_middle = middle; };
 	core::rect<s32> getMiddleRect() const { return m_middle; };
 
@@ -30,6 +32,7 @@ class GUIAnimatedImage : public gui::IGUIElement {
 
 private:
 	video::ITexture *m_texture = nullptr;
+	bool m_scale_image = false;
 
 	u64 m_global_time = 0;
 	s32 m_frame_idx = 0;
diff --git a/src/gui/guiFormSpecMenu.cpp b/src/gui/guiFormSpecMenu.cpp
index a635cda48..ca026aca5 100644
--- a/src/gui/guiFormSpecMenu.cpp
+++ b/src/gui/guiFormSpecMenu.cpp
@@ -831,6 +831,7 @@ void GUIFormSpecMenu::parseImage(parserData* data, const std::string &element)
 
 	e->setTexture(texture);
 	e->setMiddleRect(middle);
+	e->setScaleImage(middle.getArea() == 0);
 
 	auto style = getDefaultStyleForElement("image", spec.fname);
 	e->setNotClipped(style.getBool(StyleSpec::NOCLIP, m_formspec_version < 3));

[sfan5]

LGTM (not tested)