This adds a bunch of missing mailmap entries for many people. These are
needed when using rust-lang/team information in rust-lang/thanks, as the
emails there may differ.

These are all the "easy" ones, where there was a mailmap entry already,
making it clear which one is the preferred email address.

The people updated in this commit have contributed under different email
addresses than the ones they have used in rust-lang/team.

A new change will use team data for thanks reviewers, which requires this to be in
sync.
Therefore, I have updated many of the people that I've noticed being
duplicated after the change.