Async sequence, ES module support and operator updates

[ACertainCoder]

This PR adds support for use of async functions via the dedicated AsyncSequence, updates the project to support ESM and use up-to-date dependencies and adds/updates/fixes some operators.

Added:

• ESM support (in addition to CJS and UMD)
• AsyncSequence (support for asynchronous operators via the AsyncIterator)
• filterHolistically (filter all elements as a whole - similar to Array#filter; could be removed if Sequency should be limited to functions provided by the Sequences API of Kotlin)
• onEachIndexed (new intermediate method of Sequences API)

Updated:

• Project config (package manager specification for corepack, dependency updates, switch to ts-jest, ...)
• More advanced/granular type declarations in many places
• Detailed description for JoinConfig
• filterNotNull uses != instead of !== to filter out null as well as undefined
• Comparator and ComparatorFactory are now complete classes, which makes it better readable

Fixed:

• compareByDescending (null values could cause an error)

[ACertainCoder]

Closes #23