Some internal polishing is needed in the QASM3 exporter

[1ucian0]

This is a #6565 follow up

This particular issue tracks:

• The GlobalNamespace._data is horrendous and needs to be split. More here.
• Merge GlobalNamespace and Exporter.
• Better Namespace validation and renaming, see here and here.

[Ryand1234]

Hi @1ucian0, Can I work on this?

[jakelishman]

Hi @Ryand1234! This might not be the best choice for an external contributor, sorry - this issue is mostly a tracker for the core team, because we'll be making fairly heavy changes to the QASM 3 processing in Terra over the next few release cycles, and these changes will be part of it. The changes needed for this issue are very major to a core deliverable in Terra 0.20 which will have quite a lot of activity, so it'll be a bit easier for us to manage if we keep this internal.

If you're looking for good issues, we have the "good first issue" label for issues that are good for first-time contributors, and the "help wanted" label for those with a bit more experience. There's also "short project", and these may require a fair amount of physics knowledge to handle.

[jakelishman]

#12776 addresses all the problems tracked by this issue. There's still obviously polishing that could be done, but I've marked this issue as closed by #12776.