Merge branch '175-fix-opaque-type-indexing-atomic-counter-tests' into 'master'

ShaderExecutor: read counter values from the buffer

Problem: At vktOpaqueTypeIndexingTests.cpp:1077, the tests creates a std::vector called counterValues and default-initializies. Then, in the loop below, it checks counterValues as if it contains the actual counter values even though they are never read from the buffer.

Solve: Read back the counter values from the buffer.

Fixes #175

See merge request !291