Rename "object safe" to "dyn compatible"

[fmease]

Supersedes #1512: In line with T-lang's latest resolution.

Part of rust-lang/rust#130852.

r? @traviscross

[fmease]

std/keyword.dyn.html:13: broken link fragment #object-safety pointing to reference/items/traits.html
cargo/print.html:9654: broken link fragment #object-safety pointing to reference/items/traits.html
cargo/reference/semver.html:1354: broken link fragment #object-safety pointing to reference/items/traits.html

Alright, so am I meant to update the links in std & cargo before this PR gets merged? Apparently, linkchecker doesn't like the JS URL rewrites. If I were to update std & cargo first, wouldn't this mean that these links would actually be broken until the next r-l/rust books sync (*)? I've intentionally left all #object-safe links intact everywhere (library, compiler, rustdoc) to avoid this exact scenario.

(*) Or actually until the sync hits stable because std (..) links to the stable version of the Reference, not the nightly one and not channel-dependently?

[ehuss]

Thanks!

I pushed some small changes, in particular to fix the linkchecker. When there are other books that link to something, we have to temporarily include an HTML tag to hold the identifier. I will eventually try to get the other books updated.