Callbacks: exec invoke & modal now use a typed enum wmOperatorStatus.
This helps avoid mistakes returning incompatible booleans or other
values which don't make sense for operators to return.
It also makes it more obvious functions in the WM API are intended
to be used to calculate return values for operator callbacks.
Operator enums have been moved into DNA_windowmanager_enums.h
so this can be used in other headers without loading other includes
indirectly.
No functional changes expected.
Ref !136227
Listing the "Blender Foundation" as copyright holder implied the Blender
Foundation holds copyright to files which may include work from many
developers.
While keeping copyright on headers makes sense for isolated libraries,
Blender's own code may be refactored or moved between files in a way
that makes the per file copyright holders less meaningful.
Copyright references to the "Blender Foundation" have been replaced with
"Blender Authors", with the exception of `./extern/` since these this
contains libraries which are more isolated, any changed to license
headers there can be handled on a case-by-case basis.
Some directories in `./intern/` have also been excluded:
- `./intern/cycles/` it's own `AUTHORS` file is planned.
- `./intern/opensubdiv/`.
An "AUTHORS" file has been added, using the chromium projects authors
file as a template.
Design task: #110784
Ref !110783.
