Give formal index a proper title.
Use `Pass::formatted_help()` to assign the group, but still return `false` because the help text still comes from `Pass::help()`.
Tidy up some of the affected files' includes to make use of the shared `yosys.h` includes.
Update experimental pass warnings to use a shared function. Reduces repetition, and also allows all of the warning flags to be combined (which at present is just experimental and the new internal).
Update `test_*` passes to call `internal()` in their constructors.
Content is now added to the `ContentListing` rather than the `PrettyHelp`.
`open_*` methods return the `ContentListing` that was added instead of leaving a hanging continuation.
This allows for (e.g.) options to be added directly to optiongroups, instead of requiring that groups be closed before continuation.
This also means that all `PrettyHelp`s are a listing, with the actual log being called by the default `Pass::help()`; making the mode field redundant.
Added `PrettyHelp::log_help()` which replaces the `PrettyHelp::Mode::LOG` logic.
Added `ContentListing::back()` which just returns the last element of the underlying content vector.
Some of the content tracking was made redundant and removed, in particular `PrettyHelp::_current_listing` and `ContentListing::parent`.
Converted `ContentListing` to a class instead of a struct, adjusting constructors to match.
Added `ContentListing` constructor that accepts a `source_location`.
Update `HelpPass::dump_cmds_json()` for new log_help.
Define `PrettyHelp` class with methods for declaring different parts of help message.
Currently able to produce standard help messages as expected.
Updates chformal to use (only) the new help_v2.
Currently makes use of a global static to track the current help context, allowing register.h to live in blissful ignorance and instead rely on help_v2 implementations calling `auto *help = PrettyHelp::get_current();` and `return true;` to minimise impact on rebuilds (i.e. not requiring every source file to be recompiled).
