qsb: Keep the native-shader-info data when storing Metal bytecode

replaceShaderContents() moves the native resource binding map and the
separate-to-combined image sampler mapping table from the original key
to the new one, but not the native shader info. The MSL-specific data
was therefore lost whenever -t/--metallib replaced the MslShader entry
with a MetalLibShader one.

That data is not optional: the Metal backend looks up the extra buffer
bindings for tessellation and for the buffer size buffer, and asserts on
their presence.

Pick-to: 6.12
Change-Id: I79cb4dd94d65a3290afb5dbcb14900c6b120d67b
Reviewed-by: Andy Nichols <andy.nichols@qt.io>