Split the `InlineHelpers` pass into the three phases:
- `link-helpers-to-inline` links the missing `revng_inline` helper
bodies from the `libtcg-helpers-to-inline-arch` module.
- `inline-helpers` inlines, in every function except those tagged
`Root` or `Helper`, the calls to `revng_inline` helpers whose
critical arguments on the call site are constant.
- `delete-helper-bodies` drops from the module the body of every
`revng_inline` function, leaving only the declaration.
The three passes live in a dedicated `revngInlineHelpers` library
(`lib/InlineHelpers/` + `include/revng/InlineHelpers/`), so that
libraries which do not depend on `revngFunctionIsolation` can use them
without creating cyclic dependencies.
Andrea Gussoni