bytecode: Add `OBJECT_TYPE_{UN,}SIGNED_ENUM` type

Enumerations are currently converted to their integer counterparts as
soon as they are encountered.

In order to use them in captures, we need to differentiate the
enumerations from integers for the entirety of the interpretation.

This commit adds the `OBJECT_TYPE_SIGNED_ENUM` and
`OBJECT_TYPE_UNSIGNED_ENUM` to keep track of these objects.

Signed-off-by: Francis Deslauriers <fdeslaur@gmail.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I4b3ec8187a578ddc6c9d87f72d462441ba5e4a1e