The patch adds a simple framework to test the File Output Node in the compositor. The main difference to the existing `render_test.py` framework is that multiple output images are supported. Edge cases such as empty output or too many outputs are supported as well.
Tests can be run like other compositor tests, e.g. `ctest -R compositor_cpu_file_output --verbose` or `BLENDER_TEST_UPDATE=1 ctest -R compositor_cpu_file_output` to update failing tests.
Sample output:
```
...
119: [ RUN ] Running test single_color...
119: [ PASSED ] Passed
119: [ RUN ] Running test png_passes...
119: [ PASSED ] Passed
119: [ RUN ] Running test mixed...
119: [ FAILED ] Test directory /home/guest/blender-git/blender/tests/data/compositor/file_output/mixed does not exist
119: [ RUN ] Updating test mixed...
119: [ RUN ] Running test no_files...
119: [ PASSED ] Passed
...
```
Parent task: https://projects.blender.org/blender/blender/issues/125893
Pull Request: https://projects.blender.org/blender/blender/pulls/133663
0db8710df7