Refactor codegen components to prepare for benchmark generation (#5560)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/5560

## Context

Refactor operator test code generation scripts, such that components can be re-used to generate operator benchmarks.

In broad strokes, the refactors implemented by this diff are as follows:

* Improve granularity of Python modules
* Replace `test` with `correctness_test`, to make it clear that we are generating correctness tests. **Note that I haven't changed the top level target name `compute_graph_op_tests_bin` since I believe it would be too verbose.
ghstack-source-id: 244283559
exported-using-ghexport

Reviewed By: nathanaelsee

Differential Revision: D63286131

fbshipit-source-id: 1177ea381e6381045f1c97491dd7ec006690f574