On rolling distros the usage of `libpng` submodule makes problems as the
`zlib` system dependency of said module gets updated. Then the submodule
regularly is too old to handle the updates `zlib` dependency.
Fix this maintenance churn by requiring `libpng` as system library as
well. Then the distros package manager keeps those versions in sync.
This unfortunately requires users to install a new runtime/build
dependency, but it still can be disabled with `-DWITH_PNG=OFF`.
The `BUILD_RESOURCES` option is also available in `InfiniTime`, but we
don't want to require building the firmware to test `resource.zip` file
generation.
Add helper to modify spi raw file, to make experimenting with it easier.
```sh
$ ./littlefs-do --help
Usage: ./littlefs-do <command> [options]
Commands:
-h, --help show this help message for the selected command and exit
-v, --verbose print status messages to the console
stat show information of specified file or directory
ls list available files in 'spiNorFlash.raw' file
mkdir create directory
rmdir remove directory
rm remove directory or file
cp copy files into or out of flash file
settings list settings from 'settings.h'
```
In the process restructure the CMake file for less duplicate
includes/defines for both executables (`infinisim` and `littlefs-do`).
Upload the `littlefs-do` binary built by the CI additionally to the `infinisim` binary.
Use the updated upload-artifact@v3 template to do that.
