Until now, these were only transitively tested in concrete plugin
implementations, meaning that if the base implementation would have an
error (such as accessing a null optional), it would only get discovered
when building a plugin, worst case a plugin in a completely different
repo.
Consistently with changes done to Utility::Path, this enforces proper
error handling on user side. Originally I didn't want to do this and
instead wanted to have a special Array instance devoted for an error
state, but that still would allow the error state be errorneously
treated as a successful but empty array.
For file opening there's no longer an unatomic pair of exists() +
read(), but since Path::read() now returns an Optional, it means we can
reliably distinguish between empty files and failures.
While at it, also added TODOs for removal of the StringStl.h header
that's needed in various places for compatibility with APIs still using
STL strings.
It should be input first, output second, like with all other APIs. I
remember I was trying something else here, but that didn't really make
sense in the end. Also took that opportunity to get rid of one
std::string.
The original signature is a deprecated alias to the new one and will be
removed in a future release.
There will be Flag::FlipY for images at some point, enabled by default
for compatibility with existing GL code, and so it makes sense to start
discouraging setFlags() as early as possible to avoid people resetting
the default by accident.
Also update the imageconverter, sceneconverter and shaderconverter utils
to use these instead of setFlags().