Fix broken link to debugInvertOversizedImages documentation (#12662)

This PR changes the link from
https://api.flutter.dev/flutter/painting/debugInvertOversizedImages.html
to
https://api.flutter.dev/flutter/rendering/debugInvertOversizedImages.html
for the DevTools inspector documentation, according to the discussion in
the linked issue. I also changed the link in the `legacy-inspector.md`
page, as the issue persisted there too.

Fixes #12638

Author: iakdis

src/content/tools/devtools/inspector.md

@@ -520,7 +520,7 @@ void showOversizedImages() {
 
 You can learn more at the following link:
 
-- [Flutter documentation: debugInvertOversizedImages]({{site.api}}/flutter/painting/debugInvertOversizedImages.html)
+- [Flutter documentation: debugInvertOversizedImages]({{site.api}}/flutter/rendering/debugInvertOversizedImages.html)
 
 [render box]: {{site.api}}/flutter/rendering/RenderBox-class.html
 

src/content/tools/devtools/legacy-inspector.md

@@ -449,7 +449,7 @@ void showOversizedImages() {
 
 You can learn more at the following link:
 
-* [Flutter documentation: debugInvertOversizedImages]({{site.api}}/flutter/painting/debugInvertOversizedImages.html)
+* [Flutter documentation: debugInvertOversizedImages]({{site.api}}/flutter/rendering/debugInvertOversizedImages.html)
 
 [render box]: {{site.api}}/flutter/rendering/RenderBox-class.html