Avoid instantation of class with type mixed during mapping

[danog]

Some PHP 8+ coding standards require the specification of a typehint in all parameters of all functions, even if it's just a mixed typehint.
Unfortunately, the library treats mixed typehints as a concrete class type, trying to automatically map passed objects.
This is undesirable for methods like LSP's executeCommand, which takes an LSPAny = LSPObject | LSPArray | string | integer | uinteger | decimal | boolean | null arg, essentially equivalent to a mixed type.

This library already supports skipping by not providing a typehint: this PR allow skipping mapping by also providing a mixed typehint.

[danog]

Could I also get a tag after the merge please?
I need this for Psalm v6.

[DannyvdSluijs]

Maybe good to know this repo is kind of dead. The sole maintainer doesn’t seem to be active anymore. Also see #59 (comment)