fix: allow_attributes false negative on attributes with whitespace

[vishnupoddar12]

The [allow_attributes] lint false-negatived (failed to trigger) on attributes that contained internal whitespace, such as #[ allow ( dead_code ) ].

This happened because clippy_utils::is_from_proc_macro relied on strict string matching (e.g., expecting exactly #[allow), which fails if there are spaces.

Solution:

I have updated clippy_utils::is_from_proc_macro to support flexible whitespace matching.

1. Added Pat::Attr(Symbol).
2. Updated span_matches_pat to strip #[ and trim validation whitespace before checking the name.

Verified with a new test case in tests/ui/allow_attributes.rs.

Fixes #16491

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changelog: [allow_attributes]: correctly detect attributes with internal whitespace

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[llogiq]

Looks good to me. Thank you!

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