Add block_scrutinee lint

[shivendra02467]

This PR introduces a new late pass lint to catch scrutinees unnecessarily wrapped in blocks on older editions, preventing unintended behavior regarding temporary lifetimes.

Fixes #16827

changelog: new lint: [block_scrutinee] to warn on scrutinees wrapped in blocks in older editions

[rustbot]

r? @llogiq

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[github-actions]

Lintcheck changes for eed7c9c

Lint	Added	Removed	Changed
clippy::block_scrutinee	140	0	0

This comment will be updated if you push new changes

[rustbot]

This PR was rebased onto a different master 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.