Enable `png` based `ico` files and streams to be loaded into `Bitmap`

[elachlan]

In PR #11375 we discovered that when converting bmp based ico resources to be png based, there was a failure when loading the icons as the ToolboxBitmapAttribute tries to create the resource as a bitmap. This errors out as bitmap uses different PInvokes from Icon, with Icon PInvokes supporting png for a few windows versions.

This would enable us to convert the ico files to be png based, saving a few megabytes in an AOT compiled app (#11370).

[merriemcgaw]

In all likelihood we won't be able to address this in 9, so moving it to 10