fix T66899: Collada: Shininess/Reflectivity not handled correct

Fixed: The Collada Exporter only supports export of
Lambert Shaders. But Shininess is not supported with
Lambert Shaders. The exporter must not add Shininess
to the Shader data!

Fixed: The Collada Importer adds an illegal value of -1
for reflectivity when this parameters is not defined in
the imported collada data. Now reflectivity is only
set when the import data contains a valid value.

Discarded: The Collada Importer handles shininess in a
dubious way. I have discarded import for now.
This needs to be reworked carefully in 2.81.

Differential Revision: https://developer.blender.org/D5262

fix T65576 collada exporter duplicates node tree when exported material already uses nodes

fix T65480: Collada exporter did not export image texture for Base Color

update Collada Importer: reworked export and import of Materials

- added import of transparency and emission into principled BSDF Shader
- added support for importing all default collada material parameters

* diffuse
* emission
* index_of_refraction
* shininess (mapped to BSDF Roughness)
* reflectivity (mapped to BSDF Metallic)
* transparency + transparent mapped to BSDF Alpha)
* ambient (creates unconnected texture node)
* specular (creates unconnected texture node)
* reflective(creates unconnected texture node)

- added support for exporting collada material parameters:

* diffuse
* emission
* index_of_refraction
* shininess (mapped to BSDF Roughness)
* reflectivity (mapped to BSDF Metallic)
* transparency + transparent mapped to BSDF Alpha)

- prepared support for exporting the following parameters
but currently commented out:

* ambient (creates unconnected texture node)
* specular (creates unconnected texture node)
* reflective(creates unconnected texture node)

Problem: For now we only allow export of principled BSDF based
materials. I am not sure from where to get ambient, specular
and reflective as those values are not included in the
principled BSDF Shader (wip).

fix collada: get Alpha and Emission from principled BSDF Shader

fix collada Importer: Set bone transformation type when importing unskinned skeleton

fix: enforce transform export as <matrix> when exporting animated armature"

Currently we can not export Decompsed Transforms in combination with
Armature asnimations. As a temporary workaround enforce export
of transformations as Matrix for armature objects.

refactor: use Quat and BCQuat instead of float[4] arrays for Quaternions (wip)

fix T34062 Collada exporter: changed order of export for decomposed transformation.

1.) The Blender order of applying transforms is:

Scale
Rotation
Transformation

Reasoning: This order ensures there is no shearing, which happens
when you do scaling after rotation, see also:

https://blender.stackexchange.com/questions/1806

The Collada exporter now exports in the order how the transforms
need to be applied upon import.

2.) Also removed obsolete #if 0 lines

refactor collada: Added utility functions bc_string_before() and bc_string_after()