Add runtime type access via callWithReflectedType

[alessandro-amos]

Adds support for accessing the reflected type at runtime through a new callWithReflectedType API.

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[alessandro-amos]

Well, I thought it was better and ended up creating a pull request about #349, as a different solution for #252.

[eernstg]

Wow! I won't get around to it today, but I'll review it on Monday.

[eernstg]

Oh dear, time flies like an arrow, and there was another PR (#346) in the pipeline. However, #346 has now been landed, so we can proceed with this one.