SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
With a little help (read: copy & paste) from ImageWidget, QuickShow will
now cycle through the frames of animated images - enjoy the cat GIFs!
Future improvement: cache decoded images like LibWeb's ImageResource to
waste less CPU - the same applies to LibGUI though, maybe we can put
something shared in LibGfx.
Closes#5837.
The image decoder already tells us whether the image is animated and it
can provide more than one frame, let's not put this behind an artificial
"file path must end with lowercase .gif" barrier.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
