ComplexTextController: Make CheckedRef members const

https://bugs.webkit.org/show_bug.cgi?id=294050
rdar://problem/152609927

Reviewed by NOBODY (OOPS!).

This should be enough to remove ComplexTextController.cpp
from UncheckedCallArgsCheckerExpectations once [1] on the
static analyzer gets resolved.

We have 2 remaining failures here due to [1] regarding members of TextLayout.

* Source/WebCore/platform/graphics/ComplexTextController.h:

[1] llvm/llvm-project#142485

Author: vitorroriz

Source/WebCore/platform/graphics/ComplexTextController.h

@@ -201,8 +201,8 @@ class ComplexTextController {
 
     SingleThreadWeakHashSet<const Font>* m_fallbackFonts { nullptr };
 
-    CheckedRef<const FontCascade> m_fontCascade;
-    CheckedRef<const TextRun> m_run;
+    const CheckedRef<const FontCascade> m_fontCascade;
+    const CheckedRef<const TextRun> m_run;
 
     unsigned m_currentCharacter { 0 };
     unsigned m_end { 0 };