Converted `emoji.js` to TypeScript by adding relevant type definitions,
also modified `target` option in our tsconfig to 'ESNext' so that types
for object methods like `hasOwn` which is being used in `emoji.js` are
included.
This is a prep commit for typescript migration of `emoji.js`. This
commit refactors the code for generating emoji rendering details such
that we avoid writing an ugly code which will involve writing an
incomplete type object when we migrate to TypeScript.
This lets us simplify the long-ish ‘../../static/js’ paths, and will
remove the need for the ‘zrequire’ wrapper.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
