nir: Validate after deserialization.

It's a particularly relevant place for NIR bugs to occur, and if you make
a mistake in this code it gets caught in your debug build in something
like mesa/st's call to nir_split_var_copies() during finalization, which is
rather misleading.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11860>

src/compiler/nir/nir_serialize.c

@@ -2102,6 +2102,8 @@ nir_deserialize(void *mem_ctx,
 
    free(ctx.idx_table);
 
+   nir_validate_shader(ctx.nir, "after deserialize");
+
    return ctx.nir;
 }