Remaining API Annotations updates for GHC 8.8

This is a combination of four commits, each closing one of the following trac issues

#16230 (closed), #16236 (closed), #16265 (closed), #16279 (closed)

Note: #16265 (closed) includes an update to the haddock submodule, which will have to move out of the wip/ tree when merging.

It also supersedes !258 (closed) and !278 (closed) as those patches are included here.

DO NOT SQUASH on merge.