fix: preserve closure receivers for postfix chains

[mgalore]

Summary

• preserve the closure receiver when formatting field, await, use, and postfix-yield chains after a range
• add regression coverage for all affected postfix forms

Fixes #7011.

Testing

• cargo test
• RUSTFLAGS="-D warnings" cargo test
• cargo run --bin rustfmt -- --check src/chains.rs
• git diff --check

[ytmimi]

We can't just flip this from false to true for all of the variants listed It doesn't apply for ExprKind::Try. Also, as I mentioned in #7011 (comment) we should consider renaming is_method_call_receiver since that doesn't really apply now that we're also using that field for field, await, use, and postfix yield.

View changes since this review

[ytmimi]

I don't think this is supposed to apply to ast::ExprKind::Try

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[mgalore]

@rustbot ready

[mgalore]

Addressed the review in the current head: ExprKind::Try is explicitly kept out of the postfix-receiver path, and the field has been renamed to is_postfix_receiver. The issue-7011 source/target fixture covers the distinction (?.field remains unparenthesized while field/await/use/postfix-yield are parenthesized). Re-ran cargo test system_tests -- --nocapture (729 system fixtures passed) and verified the formatter output matches the target fixture.