Add Doxygen YouTube embed alias

For embedding YouTube videos in the HTML documentation without creating redundant HTML blocks.

Author: dmadison

docs/Doxyfile

@@ -261,7 +261,7 @@ TAB_SIZE               = 4
 # with the commands \{ and \} for these it is advised to use the version @{ and
 # @} or use a double escape (\\{ and \\})
 
-ALIASES                =
+ALIASES                = youtube_embed{1}="@htmlonly<div><div style=\"position:relative;padding-top:56.25%;\"><iframe src=\"\1\" title=\"YouTube video player\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture\" allowfullscreen style=\"position:absolute;top:0;left:0;width:100%;height:100%;\"></iframe></div></div>@endhtmlonly"
 
 # Set the OPTIMIZE_OUTPUT_FOR_C tag to YES if your project consists of C sources
 # only. Doxygen will then generate output that is more tailored for C. For