Consider using `reload` instead of `back_forward` for "tab restore"

[noamr]

Tab-restore describes the condition where the browser is loaded and decides to navigate to certain tabs that were open before it was closed.
This is defined in the HTML spec as "performing a reload navigation of a null document".
It's special-cased in the HTML spec to use back_forward in navigation timing... reload is arguably more accurate and suitable.
See https://bugs.chromium.org/p/chromium/issues/detail?id=1489567

If we resolve on this, the change would be in the HTML spec.

/cc @yoavweiss

[noamr]

Making the case to keep it as back_forward, and also to expose it as back_forward in the navigaiton API: whatwg/html#9941 (comment)