WIP: Enable Wswitch-enum on GCC and Clang to catch unhandled cases

[ihnorton]

This PR adds -Wswitch-enum to the compile options for TileDB core objects. With this option the compiler will warn on unhandled enum cases in a switch statement even when a default case is present`. This highlighted a few small issues which are fixed in this PR.

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TYPE: IMPROVEMENT DESC: Enable switch-enum on GCC and Clang to catch unhandled cases