Blender Git Loki

Harden checks in datatoc_icon binary

The goal of the change is to perform check for attempts of icons
being overwritten on canvas. The check is based on checking original
coordinate of icons against all read icons. If there are two icon
files which have same original an error will be reported. The report
includes both file names to make it easier to troubleshoot.

This change will allow to early-on catch issues which we currently
have with the release environment: official Linux builds might have
different icon from Blender compiled locally. This is because the
order in which directory listing is traversed is not defined, so
it's like a race condition between two files to win the place in
the final canvas.

There is still possible improvement in the code to move more fields
into the context structure. This is beyond of goal of this change.

Note that before committing this change icons must be brought back
to their consistent state. Otherwise the build will fail.

Differential Revision: https://developer.blender.org/D9715