[SPIR-V] Move check to verify PatchConstant output patch element count to Sema

[Keenuts]

The DXIL backend checks the PatchConstant output patch element count. This is not checked on the SPIR-V backend.

This means we accept code DXIL doesn't. This should not happen, and in this case, the check should be moved to Sema so both backends can benefit from it.

Follow up from https://github.com/microsoft/DirectXShaderCompiler/pull/6363