feat(dev-infra): add initial //:.mailmap (#1426)

This change adds //.mailmap initialized with mappings for duplicate
names and email addresses found in the repository archive. When a
duplicate was found, the name and email were chosen preferring the
longest name for the author, and the most practical email address (e.g.
if an obvious personal and professional email address existed, the
personal address was chosen).

Duplicate names were found with the following command:

    git shortlog -se |\
awk 'match($0, /[0-9]+[ \t]+(.*)[ \t]+<.*>/, m) { print m[1] }' |\
        sort |\
        uniq -d

Duplicate email addresses were found with the following command:

    git shortlog -se |\
awk 'match($0, /<[^>]+>/) { print substr($0, RSTART+1, RLENGTH-2) }' |\
        sort |\
        uniq -d

Change-Id: Ie0280ee336098c080cf5af8062dae20cb7a41e8e