ext_external_objects: allow buffer modifications
Earlier expectation of this test was that glBufferSubData is not supposed to work since mapping the buffer is prohibited by the spec. However while spec explicitly prohibits mapping via MapBufferRange and MapNamedBufferRange, it does not prohibit buffer updates via glBufferSubData.
This commit changes test to create empty buffer at VK side, import that to GL, update it with checkerboard pattern, render with buffer to the display and verify results.
Signed-off-by: Tapani Pälli tapani.palli@intel.com