Sync #pragma shader_stage(<stage>) to -fshader-stage=<stage>

[LBV2012-26]

This PR synchronizes the shader stages flags for the -fshader-stage= option with the #pragma shader_stage(<stage>) list in glslc/src/main.cc. Such as raygen, closest, etc.

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[dneto0]

I think it's a bad idea to make new conventions for shader stage names that are aliases of existing names.

Let's stick to the conventions in Glslang:

https://github.com/KhronosGroup/glslang/blob/ce138e2c2d6992b31ff4cd2e955904637785a881/README.md?plain=1#L80

Also, updates like this should come with tests.

[dneto0]

see comments on the main part of this PR

[LBV2012-26]

I think it's a bad idea to make new conventions for shader stage names that are aliases of existing names.

Let's stick to the conventions in Glslang:

https://github.com/KhronosGroup/glslang/blob/ce138e2c2d6992b31ff4cd2e955904637785a881/README.md?plain=1#L80

Also, updates like this should come with tests.

Thanks for your response. But it's not the new aliases. Actually it's the same as custom pragma directives of shaderc (in libshaderc_util/src/shader_stage.cc), such as #pragma shader_stage(raygen). In addition, the tesseval and tesscontrol are also not defined by glslang.
I submit this PR is not intended to define a new alias. Currently, glslc --help completely omits all ray-tracing and mesh shader stages (like rgen, rahit, etc.), even though they are fully supported in the code. I want to fix the outdated -fshader-stage help text while also standardize the behavior of the strings accepted by #pragma shader_stage() and the CLI flags.
If you still think is improper I can close this PR. But please fix the inconsistent behavior between toolchain and the commands.
Test suite I'll commit later.