use cbuilder for tuple/object generation (#24145)

based on #24127

Needs some tweaks to replace the other `struct` type generations, e.g.
seqs, maybe by exposing `BaseTypeKind` as a parameter. C++ and
codegenDecl etc seem like they are going to need attention.

Also `Builder` should really be `distinct string` that one has to call
`extract` on, but for this to be optimal in the current codegen, we
would need something like:

```nim
template buildInto(s: var string, builderName: untyped, body) =
  template `builderName`: untyped = Builder(s)
  body

buildInto(result, builder):
  builder.add ...
```

but this could be a separate PR since it might not work with the
compiler. The possibly-not-optimal alternative is to do:

```nim
template build(builderName: untyped, body): string =
  var `builderName` = Builder("")
  body
  extract(`builderName`)

result = build(builder):
  builder.add ...
```

where the compiler maybe copies the built string but shouldn't.

---------

Co-authored-by: ringabout <43030857+ringabout@users.noreply.github.com>

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