Update man page with the new options

This pull request updates the rustc manual page to represent post-#19900
state of rustc options better.

A bit unrelatedly, --help output is changed to fix some issues too:
  * -g and -O descriptions were changed from deprected flags to the new
    codegen flags.
  * dep-info value was moved from crate-type to emit flag.

Fixes #20111
Fixes #20131