Ignore str::len() in or_fun_call lint.

[Sciencentistguy]

changelog: Changed or_fun_call to ignore str::len, in the same way it ignores slice::len and array::len

Closes #6943

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @flip1995 (or someone else) soon.

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[phansch]

r? @phansch

[phansch]

@bors r+ thanks!

[bors]

📌 Commit 45e7756 has been approved by phansch

[bors]

⌛ Testing commit 45e7756 with merge b80903b...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: phansch
Pushing b80903b to master...