Test uses of functions that return function pointers with bounds-safe interfaces

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc#281

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The compiler crashed when signal with a bounds-safe interface was called in a checked scope. PR checkedc/checkedc-clang#483 fixes this. This change adds more tests of type checking of function that return function pointers, including testing uses in and outside of checked scopes.