Backport: release: Fix projection matrix computation in VR
Fix all mappers that use the VCDC matrix, e.g. GPUVolume, PointGaussian;
The VCDC matrix must be transposed before being sent to the GPU. Also make sure that GetKeyMatrices is idempotent, and remove useless calls to it.
(cherry picked from commit 86da7ae4 fomr !9620 (merged))
Edited by Mathieu Westphal (Kitware)