Duration constructor accepts weeks (unsupported in FEEL)

[barmac]

Describe the Bug

The FEEL duration accepts years, months, days, and time. This does not include weeks, even though ISO8601 allows it.
The overly support results in expressions which should result in null according to the FEEL spec, but they work fine in feelin.

Steps to Reproduce

https://nikku.github.io/feel-playground/?e=%7E3YCAkIDtgICAgICAgIC9AgCXnLAMiH3ETPlLql28AtuoufnzVGn0EWcp6S7ROtd6ssKVKZ3yv2XGPLxKZSQuxYWFiWvSMp2%2FuUaJ%2FyJMb7DpSC4VHMV1%2FYG0BBmaF%2Bn18Gb%2Ff0PkIIA%3D&c=%7E3YCAkIC%2BgICAgICAgIC9AgCXnLILCNLEWVvD4A7RTE6e5VQHnL67RAf8ffGpOTFExGjxp2lIHt%2Fmy8diAzMQSsxIFwmdegBxI7oRrX98i6CA&t=expression&st=true

Expected Behavior

The expression result should be null.

Environment

• Host (Browser/Node version), if applicable: [e.g. MS Edge 18, Chrome 69, Node 10 LTS]
• OS: [e.g. Windows 7]
• Library version: [e.g. 2.0.0]

[nikku]

Thanks! This is because we insufficiently tell apart date time from date values within the interpreter. Fixing that would address #49, too.