Fix T69090: Collada Exporter now exports the base color if Nodes are disabled

I also changed the Collada importer scuh that the diffuse Alpha is now set
for the generated PBSDF Shader AND for the base color.

Note: we can not export the base color AND the color
from the PBSDF Shaders at the same time. And when importing
we do not know if the color was originally coming from a base
material or from a shader. Setting them both in import seems
to give the most consistent results.

cleanup: Collada exporter: Removed misleading comments

cleanup: do no longer use deprecated Alpha channel from Shader diffuse color (use Shader's Alpha value instead)

fix T69772 Collada importer creates wrong fcurves for skeletal animation

refactor: collada importer: calculate fcurve index only once when creating an fcurve

fix: T71718 Collada: importer does not release intermediate fcurves when importing matrix animations

fix:wrong python pdb copied for Windows-VS when building for pydebug

fix: (unreported) When converting nurbs or curves to Mesh the generated UVMap is now named 'UVMap'

fix: Removed Debug statement from Collada CMakeLists. cmake now silently determines which collada library version it uses

cleanup: collada: removed unused public class variable