Fix deref field pattern suggestions and improve error messages

[chenyukang]

Fixes #146995

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[chenyukang]

it's perfect if we suggest ref mut here, but current diagnostic is better than &arg.field, because it's at least a right direction, since user will get this if apply ref fix here:

help: consider changing this to be a mutable reference
  |
7 |         Some(ref mut s) => s.push('a'), //~ ERROR cannot borrow `s` as mutable
  |                  +++