[ET-VK][ez] Improvements to GLSL codegen script (#10682)

## Changes

Fixed a bug in the caching mechanism in the `gen_vulkan_spv.py` script where changing the YAML file will not trigger a recompile.

Allow the python codegen to be applied to files other than GLSL compute shaders. One example application of this is generating header files (`.glslh` files) which can be shared among multiple `.glsl` files. This enables better code re-use and organization.

For a simple application of this, see the `reference_matmul_common.glslh` file that was added to the test compute shader library.

Differential Revision: [D74008572](https://our.internmc.facebook.com/intern/diff/D74008572/)