Bug 306787 – check-webkit-style: add checker for protect() in variable initialization

• Component: Tools / Tests
• Status: RESOLVED FIXED

[David Kilzer (:ddkilzer)]

The check-webkit-style tool should warn about using `protect()` free function when assigning to RefPtr/Ref variables, which violates SaferCPP guidelines.

Bad patterns that should trigger warnings:
```cpp
auto foo = protect(m_foo);
RefPtr bar = protect(foo());
if (RefPtr client = protect(client()))
```

Good patterns that should NOT trigger warnings:
```cpp
protect(foo)->doSomething();  // Method chaining - valid use
someFunction(protect(foo));   // Function argument - valid use
return protect(m_foo);        // Return value - valid use
```

See also: <https://github.com/WebKit/WebKit/wiki/Safer-CPP-Guidelines#do-not-call-protect-free-function-to-initialize-local-variables>

[Radar WebKit Bug Importer]

<rdar://problem/169460205>

[David Kilzer (:ddkilzer)]

Pull request: https://github.com/WebKit/WebKit/pull/57712

[EWS]

Committed 306771@main (3fa54a20c8ad): <https://commits.webkit.org/306771@main>

Reviewed commits have been landed. Closing PR #57712 and removing active labels.