Fix <unknown> queries and add more timing info to render_html
Closes https://github.com/rust-lang/rust/issues/81251.
## Fix `<unknown>` queries
This happened because `alloc_query_strings` was never called.
## Add more timing info to render_html
This still has some issues I'm not sure how to work out:
- `create_renderer` and `renderer_after_krate` aren't shown by default.
I want something like `verbose_generic_activity_with_arg`, but it doesn't exist.
I'm also not sure how to show activities that aren't on by default - I
tried `-Z self-profile -Z self-profile-args=all`, but it didn't show up.
r? `@wesleywiser`
This brings the size of `Item` from
```
[src/librustdoc/lib.rs:103] std::mem::size_of::<Item>() = 680
```
to
```
[src/librustdoc/lib.rs:103] std::mem::size_of::<Item>() = 280
```
