FixedSizedLists: Implement host side for this type

[cpetig]

The linked pull request only realized passing fixed sized lists between components, the host side and host code generator also need implementations.

Since these are relatively targeted todo!() items mind filing an issue as a tracking issue and tagging these with // FIXME(#NNNN)?

Originally posted by @alexcrichton in #10619 (comment)

[alexcrichton]

Some example test cases that currently fail: https://gist.github.com/alexcrichton/ba94b628d3d57f4ab63b4ea22863b91e