But only in the case where we know that we will need to access the Page fragments/tableofcontents.
In normal situations this will spread naturally across the CPU cores, but not in the situation where
`site.RegularPages.Related` gets called as part of e.g. the single template.
```bash
name old time/op new time/op delta
RelatedSite-10 18.0ms ± 2% 11.9ms ± 1% -34.17% (p=0.029 n=4+4)
name old alloc/op new alloc/op delta
RelatedSite-10 38.6MB ± 0% 38.6MB ± 0% ~ (p=0.114 n=4+4)
name old allocs/op new allocs/op delta
RelatedSite-10 117k ± 0% 117k ± 0% +0.23% (p=0.029 n=4+4)
```
See #10711
fa2d7adf10