Reword trait-object compatibility in rustdoc

[kornelski]

"Object Safety" is a difficult to understand jargon. I'm proposing a wording that makes it clearer it's about trait objects, and mentions dyn Trait which is the syntax that users are going to be more familiar with.

Related PR: rust-lang/reference#1512

Longer explanation: https://internals.rust-lang.org/t/object-safety-is-a-terrible-term/21025

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[fmease]

Thanks for your initiative! I do agree with all of the points raised.

However, I'd like to see some official T-lang-blessed proposal. Basically what Josh has proposed here: https://internals.rust-lang.org/t/object-safety-is-a-terrible-term/21025/13 to ensure that we update the terminology everywhere consistently and "all at once" (docs, diagnostics, rustdoc, …).

Edit: I think Josh suggested to open a proposal over at https://github.com/rust-lang/lang-team.

[bors]

☔ The latest upstream changes (presumably #126788) made this pull request unmergeable. Please resolve the merge conflicts.