Fix external links (#2716)

* Fix internal links

Some anchored internal links were broken because of changes in subtitles in the testing docs.

* Fix external links

Some things are stale or have 3 redirects since the time they were added to the docs. This CL fixes that.

Author: filiph

src/docs/deployment/android.md

@@ -52,7 +52,7 @@ Icons]({{site.pub}}/packages/flutter_launcher_icons) package.
 
 Alternatively, if you want to do it manually, here's how:
 
-1. Review the [Android Launcher Icons][launchericons] guidelines for icon
+1. Review the [Material Design Product Icons][launchericons] guidelines for icon
    design.
 
 1. In the `<app dir>/android/app/src/main/res/` directory, place your icon files
@@ -288,7 +288,7 @@ to the Play Store.
 [applicationtag]: {{site.android-dev}}/guide/topics/manifest/application-element
 [gradlebuild]: {{site.android-dev}}/studio/build/#module-level
 [versions]: {{site.android-dev}}/studio/publish/versioning
-[launchericons]: {{site.android-dev}}/guide/practices/ui_guidelines/icon_design_launcher
+[launchericons]: https://material.io/design/iconography/
 [configuration qualifiers]: {{site.android-dev}}/guide/topics/resources/providing-resources#AlternativeResources
 [play]: {{site.android-dev}}/distribute/googleplay/start
 [Issue 18494]: https://github.com/flutter/flutter/issues/18494

src/docs/development/ui/animations/hero-animations.md

@@ -671,4 +671,4 @@ The following resources might help when writing animations:
 : Describes motion for Material design apps.
 
 [MaterialRectCenterArcTween]: {{site.api}}/flutter/material/MaterialRectCenterArcTween-class.html
-[Radial transformation]: {{site.material}}/guidelines/motion/transforming-material.html#transforming-material-radial-transformation
+[Radial transformation]: https://web.archive.org/web/20180223140424/https://material.io/guidelines/motion/transforming-material.html

src/docs/development/ui/assets-and-images.md

@@ -351,7 +351,7 @@ In your Flutter project's root directory, navigate to `.../android/app/src/main/
 The various bitmap resource folders such as `mipmap-hdpi` already contain placeholder images named
 `ic_launcher.png`. Simply replace them with your desired assets respecting the recommended icon size
 per screen density as indicated by the [Android Developer
-Guide]({{site.android-dev}}/guide/practices/ui_guidelines/icon_design_launcher#size).
+Guide]({{site.android-dev}}/training/multiscreen/screendensities).
 
 ![Android icon location](/images/assets-and-images/android-icon-path.png)