Added ParameterBlock tests to ShaderCursor and fixed the writing code

[tdavidovicNV]

• Added tests with ParameterBlock to test_shader_cursor.
• Fixed a bug where ParameterBlock<T> could only be written if T was a struct.
• Disabled the ParameterBlock tests, as Vulkan validation complains about the codegen (see In mixed uniform/ParameterBlock syntax, Slang generates invalid Vulkan code slang#7431) and the results are actually wrong (in variables that are not in the ParameterBlock).

[tdavidovicNV]

This is still failing, will need closer review on MacOS

[jhelferty-nv]

@tdavidovicNV Should this be moved to draft?