PostProcessingComputePass: dangling iterators from get_resources() temporaries (found via clang 23 -Wdangling-gsl)

[windsunil]

Building with clang 23 and warnings-as-errors fails in framework/rendering/postprocessing_computepass.cpp:

framework/rendering/postprocessing_computepass.cpp:154:33: error:
object backing the pointer will be destroyed at the end of the
full-expression [-Werror,-Wdangling-gsl]

Looking at the code, I think the warning is a true positive rather than noise. PipelineLayout::get_resources() returns
const std::vector<ShaderResource> by value (a fresh copy each call), and the transition code calls it three times:

auto resource = std::find_if(pipeline_layout.get_resources().begin(),
                             pipeline_layout.get_resources().end(),
                             [&storage](const auto &res) { ... });
if (resource == pipeline_layout.get_resources().end())
    ...
const bool readable = !(resource->qualifiers & ...);

So begin() and end() come from two different temporary vectors, both are destroyed at the end of the statement, the later end()
comparison uses a third temporary, and resource->qualifiers dereferences an iterator into a destroyed vector.

It probably never crashes in practice because, as #841 noted, this class appears to be unused - but it is still compiled everywhere, so
clang 23 makes it a build failure for -Werror configurations.

Two possible ways out:

1. Call get_resources() once and keep it in a local:

const auto resources = pipeline_layout.get_resources();
auto resource = std::find_if(resources.begin(), resources.end(),
                             [&storage](const auto &res) { ... });
if (resource == resources.end())

or

2. remove the class, as framework/rendering/postprocessing_computepass is never used - should it be removed? #841 already suggested.

Happy to send a PR for option 1 if that is the preferred direction.