Implement Window::request_redraw on Android

[ghost]

This implements Window::request_redraw on Android based on the feedback given here: #1822 (comment)

• Tested on all platforms changed
• Compilation warnings were addressed
• cargo fmt has been run on this branch
• cargo doc builds successfully
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality
• Updated feature matrix, if new features were added or implemented

Fixes #1723

[msiglreith]

Thanks, please update the request_redraw documentation. It still contains a section stating it's not supported on Android. Up to my understanding this doesn't handle subsequent `request_redraw' calls after main event cleared so this should be added as platform specific.