This adds support for listener objects which, in addition to the existing callback listeners, can optionally provide a displayName ahead of time to avoid a potentially awkward humanized displayName.
This was bootstrapped with running `decaffeinate` on both command-registry
and its spec, but involved a line-by-line eyeing and updating for idioms
and, in one case, correctness:
For some reason, copying the keys to the new dispatchedEvent in
coffeescript (command-registry.coffee:235) currently does not result in a thrown
exception, as it should when trying to write over the read-only property
`isTrusted`, so I added a check to ensure that the key did not already
exist in the new event. Moreover, other definitions of `preventDefault`,
`stopPropagation` and friends, which are also enumerable afaict, would
also overwrite the ones defined just prior (command-registry.coffee:220
and command-registry.js:325), so that check ensures we don't overwrite
those either.
Test plan: `./script/lint && ./script/test`, and a lengthy smoke test of
various commands through keybindings, command palette, and package
interfaces.
Released under CC0.
