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Regression Testing: Running tests based on blend files

Runs tests based on blend files with minimum python interaction.
Developed as part of GSoC 2021 - Regression Testing of Geometry Nodes.
Earlier, tests were built from scratch by adding a modifier/operation
from the Python API.
Now, tests can also be created inside blender and are compared using
Python script.

Features: Automatically adding expected object if it doesn't exist.
This patch adds tests for the following Geometry Nodes category:
* Curves
* Geometry
* Mesh
* Points

The implemented UML diagram for refactoring of mesh test framework.
{F10225906}

Technical Changes:
SpecMeshTest: It adds the modifier/operation based on the Spec provided.
BlendFileTest: It applies already existing modifier/operation from the blend file.

Test folders hierarchy with tests. This folder should be extracted to `libtestsmodeling`
{F10240651}
Note: The `geometry_nodes` folder might lie under another `geometry_nodes` folder while extracting, please double check. Use the inner-most one.
The hierarchy should be:
-`libtestsmodelinggeometry_nodesmesh`
-`libtestsmodelinggeometry_nodespoints`
and so on.

* From `ctest` the tests should be run as `ctest -R geo_node -C [Configuration]` on Windows.
* Each single test can be run with its entire name e..g `ctest -R geo_node_geometry_join_geometry`.(just an example). Run `ctest -N -R geo_node` to see all tests.
* From blender, the tests can be run `blender -b pathtoblendfile --python pathtogeo_node_test.py`

Reviewed By: zazizizou, JacquesLucke

Differential Revision: https://developer.blender.org/D11611