Add `*Value` helper accessors in `PrimitivePathObject` and `PrimitiveInstance`

[maratal]

Add *Value helper accessors in PrimitivePathObject and PrimitiveInstance to avoid long resolution path like:

let value = try root.get(key: "myKey").asPrimitive().value()?.stringValue

Should be:

let value = try root.get(key: "myKey").asPrimitive().stringValue().

https://ably.atlassian.net/browse/AIT-1330

Originally posted by @maratal in https://github.com/ably/ably-cocoa/pull/2243#discussion_r3804602675

┆Issue is synchronized with this Jira Task by Unito

[maratal]

closed by mistake