docs: Update Presto functions coverage map (facebookincubator#12195)

Summary:
Updated the complete list of Presto scalar and aggregate functions using output from
Presto `SHOW FUNCTIONS`.

Re-generated coverage maps with instructions from `velox/functions/prestosql/coverage/README.md`.

Pull Request resolved: facebookincubator#12195

Reviewed By: kagamiori

Differential Revision: D69496939

Pulled By: kgpai

fbshipit-source-id: 0b5c85d077d9a5dccf5101a8ebca672c6f557763