feat: make let_binding_suggestion more reasonable

[Young-Flash]

This is my first PR for rustc, which trying to fix #117894, I am not familiar with some internal api so maybe some modification here isn't the way to go, appreciated for any review suggestion.

[rustbot]

r? @petrochenkov

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[fmease]

Implementation looks ok. However, I can't approve this PR since I'm only a rustdoc reviewer :')

[petrochenkov]

r=me after addressing #117934 (comment), #117934 (comment) and squashing commits.

[Young-Flash]

@rustbot ready

[petrochenkov]

Thanks!
@bors r+

[bors]

📌 Commit c710db8 has been approved by petrochenkov

It is now in the queue for this repository.

[bors]

⌛ Testing commit c710db8 with merge 4fd68eb...

[bors]

☀️ Test successful - checks-actions
Approved by: petrochenkov
Pushing 4fd68eb to master...

[rust-timer]

Finished benchmarking commit (4fd68eb): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	1.2%	[1.2%, 1.2%]	1
Improvements ✅ (primary)	-3.2%	[-3.7%, -2.7%]	2
Improvements ✅ (secondary)	-3.4%	[-6.9%, -1.1%]	3
All ❌✅ (primary)	-1.8%	[-3.7%, 1.1%]	3

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 674.644s -> 677.24s (0.38%)
Artifact size: 313.53 MiB -> 313.50 MiB (-0.01%)

[Young-Flash]

Great，thanks @petrochenkov and @fmease for patient review 😁