`std::variant` is the last archetypal container missing in TreeBuilder-v2. The
code for it isn't hugely complicated and relies on pack expansion.
This change introduces a new field to the container specification:
`scoped_extra`. This field allows you to write extra code that will be included
within the TypeHandler in CodeGen. This means it will not have collisions with
other containers, unlike the existing `extra` field. It's used here to write
the recursive `getSizeType` function for `std::variant`.
Tech debt is introduced here by comparing the container name to `std::variant`
in CodeGen to conditionally generate some code. We've worked hard to remove
references to containers in code and move them to `.toml` files. On balance,
this is worth having to include the example of `std::variant`. It should be
moved into a container spec field at some point, the design of which is still
to be determined.
Test plan:
- Activated the OIL `std::variant` tests.
- CI
Summary:
Handlers were added in an intermediate form of tbv2 but those intermediate
forms have now been removed. Remove all the handlers to make grepping/find and
replaces easier across the types.
Test Plan:
- CI
This change is fully backwards compatible with the old ContainerInfo
parser, as it is just adding new fields.
The old fields will continue to be used by legacy OICodeGen until that
is removed.
Also add a README to document the format.
