Handle intrinsics systematically (#3422)

Since compiler intrinsics are handled both in codegen and
instrumentation, it would make sense to have a single source of truth
with regard to which intrinsics we support and update it systematically.

This PR introduces an `Intrinsic` enum, which allows to parse intrinsic
name into one of the predefined variants we support or a catch-all
`Unsupported` variant.

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under the terms of the Apache 2.0 and MIT licenses.