Add an instructions argument to ConcreteBytecode, and validate its value

[eric-wieser]

Also adds validation to Bytecode

[vstinner]

I dislke the current code to validate instructions. The validation is delayed when you iterate on instructions. I would prefer to raise an error on .append(123) for example.

An option would be to modify InstrList to inherit from abc.MutableSequence instead of list, and implement the ABC using a private list. setitem() and insert() would validate that added items are instructions.

[eric-wieser]

Ok, updated with those changes.

[eric-wieser]

Aside from the abc.MutableSequence change, which would probably do better as a new PR building on this, is this good to merge?