Indexer breaking changes improvements

[baywet]

Follow up to #2594: we should drop the backward compatible string variant of the indexer we introduced
Follow up to #2978: we should avoid using a hardcoded parameter name and use the one from the description

[IEvangelist]

Hi @baywet, I was going to ask about the availability of the improvements specific to C# that would include naming the parameters of builder indexes, such that they align with the URL template. For example, generated clients seem to use a hardcoded position name, which isn't meaningful at all. It would be so much better if the name matched the name in the template, for example:

Considering the following GitHub REST API.

• Set labels for issue
• /repos/{owner}/{repo}/issues/{issue_number}/labels

It should generate a client that is compatible with the following named indexer parameters:

// URL template: /repos/{owner}/{repo}/issues/{issue_number}/labels
//    /repos
//       | /{owner}
//       |     |            /{repo}
//       |     |               |              /issues
//       |     |               |                 |  /{issue_number}
//       |     |               |                 |         |          /labels
//       ⭳     ⭳               ⭳                 ⭳         ⭳             ⭳
client.Repos[owner: "dotnet"][repo: "runtime"].Issues[issue_number: 1].Labels.*Async

I would love to see this available ASAP, and I think it would be perfectly acceptable for it to be behind the --exclude-backward-compatible.

[baywet]

Thanks for the additional context here.
I'll let @sebastienlevert comment on whether we should introduce additional behaviour behind ECB to emit the correct parameter name before the v2.

[sebastienlevert]

v2 is still something that we haven't committed to as we've been able to introduce changes without making them breaking. I'd add slide them behind ECB for now and remove when v2 is out the door.