Refactored Uniform Buffer support

Refactored Uniform Buffer support

Uniform blocks in GLES3 shaders are now supported by GPU buffer.
Fixed up test harness to handle CPU buffers properly
Fixed up test cases with wrong buffer counts

Added method to get uniform block alignment from the
backend - this is slightly more complicated than it
needs to be, because of the Vulkan-like API we have.

Enhanced test harness to enable testing of UBOs.
Adding reflection & test cases for uniform blocks

Ensured that multi-pass of draw commands doesn't
generate multiple blocks.

Ensured GPU uniform buffers are double-buffered

Ensured size of CPU/GPU for offscreen vs onscreen
buffers is correct.

Added test cases to ensure that large enough buffers
are allocated, and that properties are written
into the relevant uniform block areas within the buffers.

Change-Id: Id551d56ecea228320af3896afef49790d5ceec6d