Deprecate redundant lint option_map_or_err_ok and take manual_ok_or out of pedantic

[samueltardieu]

While extending the option_map_or_err_ok lint (warn by default, "style") to recognize η-expanded forms of Ok, as in

    // Should suggest `opt.ok_or("foobar")`
   let _ = opt.map_or(Err("foobar"), |x| Ok(x));

I discovered that the manual_ok_or lint (allow by default, "pedantic") already covered exactly the cases handled by option_map_or_err_ok, including the one I was adding. Apparently, option_map_or_err_ok was added without realizing that the lint already existed under the manual_ok_or name. As a matter of fact, artifacts of this second lint were even present in the first lint stderr file and went unnoticed for more than a year.

This PR:

• deprecates option_map_or_err_ok with a message saying to use manual_ok_or
• moves manual_ok_or from "pedantic" to "style" (the category in which option_map_or_err_ok was)

In addition, I think that this lint, which is short, machine applicable, and leads to shorter and clearer code with less arguments (Ok disappears) and the removal of one level of call (Err(x) is replaced by x), is a reason by itself to be in "style".

changelog: [option_map_or_err_ok and manual_ok_or]: move manual_ok_or from "pedantic" to "style", and deprecate the redundant style lint option_map_or_err_ok.

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[samueltardieu]

Rebased