feat(complete): Only complete flags in PowerShell when word starts with -

[MatejKafka]

In PowerShell, built-in completion system only completes parameter (flag) names when you type a - (dash), otherwise it assumes that you're entering a positional parameter value (or a subcommand). The completion script generated by clap_complete does not replicate this behavior, which feels out-of-place compared to the built-in completers.

This PR fixes the behavior to match built-in PowerShell completions.

[epage]

Note that we generally ask for Issues to be created so we can get alignment before moving onto issues. This avoids wasted time on both sides and helps provide a central point of discussion as multiple PRs may end up existing for one root cause for various reasons.

Our focus is shifting to our new completion system (#3166). While we can still improve the existing completions, I would prefer it to be done in a way that is aligned with #3166. Currently, #3166 generates all completions in a shell-agnostic way. Each shell only has a thin adapter. This means most likely that the problem exists there too.

So the question is how should we handle this in #3166.

Some options:

• Decide this is the right behavior for Stablize Rust-Native Completion Engine Tracking Issue #3166 and extend it to all shells
• Add some per-shell logic in Stablize Rust-Native Completion Engine Tracking Issue #3166
• Decide this is not the right behavior and don't change any shells in either completion system