Bug 40072: Move capture_exec to a separate module

Because the RBM and RBM::DefaultConfig modules have circular dependencies, exporting functions from RBM to RBM::DefaultConfig doesn't work, which means that part of the changes for #40068 (closed) didn't work. We could fix that by using RBM::capture_exec instead of capture_exec. An other solution is to make a separate module for capture_exec. Since the RBM modules is becoming big, I think it's a good idea to move independent parts to a separate modules.

/closes #40072 (closed)

Tested while testing the changes for #40071 (closed), doing an android build.