Support importing path-segment keyword with renaming

[mu001999]

Reference PR:

• Clarify use $crate restriction reference#2010

Description:

• Make imports consistent, self/super/crate/$crate can be imported with renaming now
  • Allow use self/super/crate/$crate as name; and also use super/crate/$crate::{self as name};
  • Deny use self/super/crate/$crate; and also use super/crate/$crate::{self};
  • Deny use ::self;, use ::{self};, use ::self as name; and use ::{self as name};
• Proper error messages, and E0430 and E0431 are no longer emitted now
  • [E0430]: self import can only appear once in an import list was emitted before when std::fmt::{self, self}, but the emitted [E0252]: the name fmt is defined multiple times is good enough
  • [E0431]: self import can only appear in an import list with a non-empty prefix was emiited before when use {self as name};, now use {self as name}; is allowed; for use {self};, it's denied because it lacks renaming and will emit imports need to be explicitly named with suggesting renaming.

Fixes #29036
Fixes #35612
Fixes #37156
Fixes #146967

r? petrochenkov

[rustbot]

Failed to set assignee to [petrochenkov]: invalid assignee

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[mu001999]

@rustbot ready

[mu001999]

@rustbot ready

[petrochenkov]

Thanks!
I'll start crater next.
@bors try

[rust-bors]

☀️ Try build successful (CI)
Build commit: 18c1d18 (18c1d185ac7a6a3bf399296b35e4b2736809a756, parent: 9050733395f7c10560d49f549e022f411fa28cea)

[petrochenkov]

@craterbot check

[craterbot]

👌 Experiment pr-146972 created and queued.
🤖 Automatically detected try build 18c1d18
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[mu001999]

@petrochenkov Thanks a ton! I appreciate you taking the time to review this.

[bors]

☔ The latest upstream changes (presumably #149462) made this pull request unmergeable. Please resolve the merge conflicts.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.