We want to use the same header in the inspector, so move it to
the toplevel. And since it is no longer for demos only, rename
it to profile_conf.h, and also rename the build option back
to profile.
In certain scenarios, address the issue where gnome.compile_resources
fails to transmit the present source directory. This is most notably
visible with MSBuild.
Determine the location to save testcases in dynamically,
trying first a GTK_SOURCE_DIR environment variable
and then the current directory as the GTK source dir,
ultimatively falling back to just saving in the current
directory.
This avoids leaking details of the build environment
into the produced artifacts and should make GTK builds
more reproducible.
Fixes: #5403
