Prepare to publish analyzer 0.31.1 and associated packages.

Verified that the new analyzer at least smoke-tests on .21 still,
so did not update SDK constraints.  Publish is to address
dart-lang/dartdoc#1603.

Change-Id: I39320e5557344f6c1c79df50b792246fc1c29840
Reviewed-on: https://dart-review.googlesource.com/40401
Commit-Queue: Janice Collins <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Reviewed-by: Devon Carew <[email protected]>